The temple of heaven - impossible rooms and treasure?

From what I've read, when the Generations EP came out, it was no longer possible for a sim to travel through such narrow passages as are in that room. When WA was made, it was possible, but they never changed the tombs after it became an issue. That isn't the only place where you'll find a too narrow passage. There's also one in Tuatha's Garden in France, which you may not have tried yet, as it is a tomb that's not on a lot, with no adventure opportunity attached to it. As far as I have figured out, there are only three ways you can get your sim into that area, which you must do to get the tomb relic, because it's in that central room.

The only non-cheat way is to have you sim meditate until they can zenoport, them have them get there that way. Of course, you'll have to either zenoport them back out again, or have them use escape dust.

The second way, the one I use, is to turn on testing cheats, shift click inside the the space around the hidden room, and teleport them in, then out again when they finish.

For the third method, turn testing cheats on again, then use the BuildBuyEnabledForLot true cheat, shift-click on the floor, and choose "build on this lot" and remove one or both of the walls of the too-narrow passages in build mode.

Oh, I think I remember that part. My very unhelpful answer: I didn't even attempt to play the Temple of Heaven without testingcheats turned on. Not because I wanted to get to the parts that were difficult to access (although that was a nice side-effect), but because I wanted to get out alive. As soon as my Sim took several of those stairways leading left and right and up and down, I had no idea where the exit was anymore! So I had no qualms about teleporting to that chest and plundering it. :)

next time I go to China I'll see if that's the one I finally figured out. If I'm in the tomb I might be able to remember what I did to open it. If it's the one I'm thinking of the switch for it is upstairs.

My sims can't pass through that narrow passage either. I've also had 2 issues in Tuatha's Garden with similarly tight spaces. I don't recall if zenport works in the China tomb, but in Tuatha's Garden there's not enough space past the restrictions to zenport to. Like @IreneSwift , I also use the testhingcheats teleport option to get past this part.

I once tried fixing it in build mode by making the passage larger, copying the lot to the bin, and using that to replace the original tomb in new games. But then later quests in that tomb were broke. So I went back to just teleporting with the testing cheats. There's no other way in.

Right, in Tuatha's garden you have to move them directly onto the floor switch, but you can only zenoport to an empty floor space.

LOL at @PalmArrow. You know, if you zoom out, you can see the entire layout, right? You can always get your bearings that way. I did that often, in quite a few of the tombs.

@IreneSwift , I know you can see the whole layout, but one floor at a time. In some tombs you explore floor by floor, but in the temple of Heaven your path would constantly lead you up and down. I guess after a while I just found it tedious to keep track of rather than an interesting challenge, so I started to just teleport everywhere. :)