Cinta: Thank you so much for that link; it led me to google for more information and I found that the Undersea Succulent Garden is on display at San Diego Botanical Gardens. I'm going to be in SD for a few days next month and I sure hope I get to the visit the gardens! I think most of these are actually outdoor gardens made to look like undersea coral reefs but it could be done on a smaller scale in a terrarium.
I also found this site ... some amazing succulent displays; I love the second photo with the metal bench and farther down the ones that resemble roses are really awesome!
