I got the idea for this one, while adapting The Immortal Heartbreaker Vampire Challenege by Vaneth to my needs.
Since the original challenge has some overlaps with one of my favourite movies, I decided to adapt the challenge to that movie, The Man from Earth.
This challenge is quite soul crushing and heartbreaking at times, but also very beautiful, in my opinion, and, depending on your nature, it can be quite a tear-jerker.

A word in advance:
This challenge requires you to have 10 different (reasonably) playable worlds at your disposal, whether these be custom worlds or from EA does not matter. You will only stay on each world for one whole generation, so if you have maps that run stable for you up to generation X, before things break down, then they are still perfectly suitable. Imaginary bonus points, if you have maps from different Eras, like Roaring Heights, or even some medieval map or the like. Look here or on the exchange. You will find medieval and 50ies themed worlds, among many others, some of them pre-populated. It really is up to you how much time passes between the individual chapters. You could even use some pre-historic, sci-fi or dystopian map.
A nice side effect of this challenge is that you might be playing maps that you have never or barely touched before, and might also interact with Sims you never encountered.
The overall length of this challenge is somewhere between 600 and 700 Sim days (ten lifetimes starting at young adult, basically, taking into account your mate's starting age on each world).

The main premise:
Due to a genetic anomaly, the main character (which I will call the protagonist) has perfect cell regeneration that will never start failing, not unlike the real-life Hydra or some Jellyfish, and stopped aging beyond a certain point. The protagonist has been around since the early days of man and is effectively immortal, but can of course still die from accidents and the like (unless you give them the unlucky trait, which is perfectly allowed).
The goal is to play through ten different episodes of the protagonist's life time. These episodes can, but don't have to be, in chronological order and how much time has passed between the episodes is entirely up to you. It would make sense to do it chronologically, due to the skills and such acquired over the run of the game.
Each of the episodes will represent a chapter of the protagonist's life, in which they found a mate, a person they decided to stay with. The protagonist is painfully aware of their inability to die from old age and as such is carrying around a reasonable amount of survivor's guilt. They also know that they have all the time in the world at their disposal, so rushing headlessly into things is not really their thing. The lives of others pass for them in the blink of an eye and people come and go like waves of grain. But we all know that love can strike at any time and even an immortal does not want to be alone forever. So, on occasion, they will find that one person they want to spend a life time with.
And a life time is all they will get, since their mates will be anything but immortal:
The Heartbreaker lifetime wish in this challenge refers more to the protagonist's heart than anyone else's, as they will repeatedly have to watch their partners age and die, and then leave everything and everyone behind. There is something devastatingly beautiful in seeing the partner die with the last unfulfilled wish being to go on another date with the protagonist.

Preparing for the challenge:
You will obviously need your protagonist, who can be any gender you like, but needs to be human (witch would reasonably work, as well, since they have the same lifespan). They can have any traits that you want, but needs to have the "Heartbreaker" life time wish (Due to the constant map changes it might not be achievable, as the game keeps track very wonkily across maps, but it doesn't matter). Starting age is highly recommended to be Young Adult, since you will need quite a bit of time to rack up the required Lifetime Points to buy the Age Freeze Potion for the whopping 65.000 points.
Activate the option "Exclude active household from celebrity system". You can keep it deactived for an extra challenge, but the protagonist is trying to stay under the radar and becoming famous is the opposite of that.
Whether you want to disable or limit the supernatural population is entirely up to you, just keep in mind that your mate will always have to be human, as well. Your protagonist will have an easier time staying undetected with other long-lived creatures on the map, if you want to explain away inconsistencies, but it's not a requirement.
If you want to play it chronologically, now is a good time to lay out your map order.
Set the Sim lifespan to 90 days, but you can adjust individual stage duration as you see fit. The total must be 90 days.
I, for example, have it set up the following way, which works quite well:



Goals:



Rules:



Scoring (absolutely optional, since the main goal is the experience):



Movie quotes for inspiration and to set the mood:




Feel free to have a eulogy for your mates here, if you feel the need to. I, for sure, have done the same and I won't judge.
I am AuDHD, so these things hit quite different and a lot harder for me.

"My beloved Feli,

I can not thank you enough for this one wonderful life that you gave and dedicated to us.
You chose the poor teacher, and you never once complained. Not, when you had to take care of the house, or our son, while I was out, teaching other people's children.
We did never live large, as you were obsessed with saving money for the retirement. And we managed.
In fact, we managed it so well, that once Emil moved out, we could buy that cottage by the sea for you.
While I never agreed with your career, I was very proud when every newspaper was full of headlines about the latest high profile heist, and I knew it was you.
The day before you retired, I quit my job, since I had reached my ceiling there anyway. I wanted to spend your last years exclusively with you.
All the following years were like an endless single date. You taught me to take nothing for granted and enjoy the small things in life. Thank you for that.

You died two days after Love Day, the day after holding your epic birthday party for our son Emil, at the age of 96. Wanda died later that same day.
I buried you in your garden, which you loved so much.
Your grandson, your son, and, most of all, your husband miss you dearly.

Tomorrow I will leave, without telling anyone. I will take with me our photos, the portrait I made of you, the videos I took of you and Emil, and the memories of a beautiful life at your side.

With endless love,
Your husband"

https://www.youtube.com/watch?v=VmBxseBs_E8

Just FYI, using Master Controller along with the Master Controller Cheats mod, you can fix the count if your LTW count gets reset. I ran into this with one of my current sims that wants to rescue 50 sims as a firefighter. Every time I reset the town, their count gets set back to 0.

nraas > Sim > Advanced > Lifetime Wish: Change Tally

Just enter in whatever the correct count is. It might take a few minutes real time for it to show up. Unpause the game if paused, switch to a different sim, switch back, and check your LTW. It should show the correct count now. If you don't have any other household members yet that you can switch to, wait a few minutes.

Indeed, that would work. It is not really essential for this challenge to actually fulfill the protagonist's lifetime wish, but if you are a completionist and would want it to trigger, using MC will absolutely work. The Heartbreaker lifetime wish in this case is more meant to give a theme and to block out the lifetime wish instead of filling it with something easily achievable. The protagonist is immortal. Would be sad if he fulfilled his lifetime wish in 10 years, cause then what is he gonna do for the rest of eternity
I mean, let's face it: By the end of this challenge you will probably have so many lifetime reward points already, you won't know what to buy with them anymore. The only real challenge in regards to the lifetime rewards is getting the initial age freeze potion, but even that is normally easily achievable in the run of the first 30-ish days, especially if you run a mod like Relativity and have the game time run at half speed, which is perfectly allowed. Just keep in mind that the overall length of the challenge is around 700 Sim days depending on your settings, so you'll be playing it for the better part of a month on half speed.

I was thinking long and hard, if I should restrict mod usage, but I believe people should play this the way they enjoy it the most and I am running a ton of mods myself. The only one you'd be cheating is yourself. Hell, I'd even be okay with people giving themselves enough points to chug that potion right away, if they so desire. The protagonist has been around for a while and did not just turn immortal yesterday. But starting the first chapter with the regular starting money and a clear goal to achieve with your lifetime points adds to the feel of that first chapter already. Also, it would make the most sense for the protagonist to have reached adult stage before downing that age freeze pot. But if you want to start out as an adult already, by all means, give yourself enough points to get that age freeze (Don't simply buy it via MC. It won't spawn in your inventory).

If people need some ideas for maps that come mostly populated (some of them as saves only), here are some that would fit.
In case you do indeed want to start the challenge on a prehistoric map, you will face some issues, however, as they usually come without any rabbitholes, so any rabbithole career is impossible to do (and also doesn't make much sense). Meaning, it will affect your scoring, if you are keeping track.
I tested all the maps, except for two, and they run smooth to decent on the Win 7 potato I run the game on.

Urduna - beautiful prehistoric world with some pre-built caves to live in, but unpopulated

calinselene's Uresh - Persia inspired world. Comes with a population save.

Rabenstein - A nicely done populated medieval world. Descriptions and location names are in German, however.

Pirate Island - As it says... a Caribbean pirate island - unpopulated, afaik

Wild Wild West revisited - Pre-populated wild west world- set around the 1920ies, I'd reckon.

Forever the 50s - Pre-populated world set in, well, the 50ies

Paris - Modern day Paris - unpopulated, afaik

Lunar Lakes - A store world set in the future on a different planet, if that's your jam

Other suitable Sims 3 (store) worlds, due to their timeless feel of not being locked to a specific decade, include, but are not limited to:

Monte Vista - a historic town in modern day Italy

Midnight Hollow - my absolute favourite! Beautifully anachronistic with a touch of Victorian Steampunk and Silent Hill. Arguably the best NPC Roster of all time in any Sims 3 world. Whether it's Lucien Hyde (based on Marilyn Manson), the Laus (based on the Powerpuff Girls), or Katarina Stewart, the living doll - these characters will stick with you.

Aurora Skies - Beautiful Scandinavian world, based on Iceland. Could honestly be used for any decade after 1940/50.

Sunlit Tides - The one functional Island map we got from EA XD

Lucky Springs - a fan favourite

Starlight Shores - Also a fan favourite

Roaring Heights - gracefully representing the roaring 20ies to 40ies