A while back I built an Egyptian Temple with the Hirst Arts molds. I liked it a lot so I decided to start building some crypts. I like the idea because they will multi-task pretty good, everything from fantasy to sci-fi.
I molded all the individual blocks from buff colored dental plaster and then sealed it with a water based clear coating. Finally, I used brown gel-stain and wiped it off for the aged effect. Considering I did this in a pretty big hurry with less care than I should have used, I still think they came out quite well.
Hirst Arts has some really cool stuff if you do not mind taking a bit of time to cast and build it. It is not hard to do, but you really need to not be in a hurry.