I'm curious about trying my hand on building tombs like those from WA. However I'm not sure where to start. I've looked into some basic contraptions once before. Stuff like: pulls this, open that. I was wondering if someone could share some advice or trips and tricks maybe?

You are in for some fun! I made quite complex multi- step puzzles for tombs in one of my worlds, where one part had to be solved before another could be accessed. The processor is your friend here, you can use boolean logic switches to create puzzles. Things like, if switch A is pulled, AND switch B, but NOT switch C, then open the door. Also use the processor to fire traps- for example, the crawling ants setting will fire sequentially.

These guides might help- the Sims Resource wiki seems to be either gone, or behind a paywall, but can be read through the Wayback Machine.
https://www.carls-sims-3-guide.com/...ombbuilding.php
https://web.archive.org/web/2014071...:_The_Processor


Edit:
I found other tomb tutorials on the TSR wiki too:
https://web.archive.org/web/2017060...mb_Creation_101
https://web.archive.org/web/2017060...Building:_Basic
This one remains unfinished:
https://web.archive.org/web/2017060...lding:_Advanced

Also I uploaded a zip of some of these tutorials in PDF form, plus a rather good one from bunbunnyny that was on the Sims 3 forums:
https://simfileshare.net/download/4164312/

Thank you for the answer! I must admit that the processor is a bit intimidating. I tried following the tutorial but I'm not confident I did it correctly.

I also did find an IGN walkthrough to building tombs. It doesn't cover the processor but from what I read it sounded OK.

I think the main thing is to have an idea of what you want to happen (for example, sims have to find a key to open a door before they can access a dive well to a secret island), and then work out how to achieve that. For most simple puzzles like that, you don't need the processor- that's more for complex problems.

Currently I'm testing out things. I want to know how things works before I start taking on something bigger. I have got two questions though. I had this idea of like a hidden tomb in a museum of sorts, so I was checking out the decorative Rory table or whatcha call it, where you can donate stuff. That made me think, what if you remove something and that activates a trap? I put down a coin pile to test but the only option I have is view, not remove. What am I doing wrong? The trigger for remove and fire once is there... all linked up.

Secondly, I thought the (!) option for treasure was supposed to do something bad... but instead it gave me a nectar worth 24k... Is that intended?

Aren't some things broken now? Since Pets? I know I could not complete some tombs in Jericho. I also tried to do a few things on a lot in a world I am working on now and could not get them to work even though I read several tutes.

I also had a problem doing treasure chests. And items on the floor under a sandpile.

I have all the EPs but the things just did not work for some reason? Maybe/probably was my errors? But I decided that it is OK as really did not plan on doing much anyway.