I am so sorry about the pitiful condition of this set. I would not have posted it here if it hadn't received over 100 downloads from my Tumblr.
Sims can walk through the pieces because the footprints do not match the parts. (You can hide objects in there to stop that if you want.)
Unfortunately the monkey ruin looks as if he is relieving himself:
But he looks much better with fountain sprayers hidden inside of him:
The little pool area at the base is open and colored in with water colored terrain paints by mammut.
I was very tired after work when I was working on these, so I really can't tell you a better reason than that, that they are found in "rocks", and they do not land evenly when plopped down, so you need to use "move objects" while placing them.
I did not decimate due to the high level of distortion when I tried to do it.
If anyone is interested in improving this set, please feel free to share it. My version can be removed if you let me know you would like to take over the project. I'm sure it would be appreciated by those playing the history challenge.