Other than the fountains, this is the best feature of the Bellagio - a gorgeous, themed conservatory full of flowers (and sometimes butterflies) that is 100% free. The first time I came here at Christmas time, everything was done up in red and white poinsettias, which were nice enough - but springtime is the real star. I've seen a butterfly theme, an Alice in Wonderland theme (with giant bees and ladybugs made out of flowers), and currently a Northeastern sort of theme with an old carousel (that runs) and a fake lighthouse with a real light. The giant ladybugs and bees are still around as well. A pair of egrets made from flowers and birdseed were new and quite realistic.
This is definitely a creative work of art, especially to be enjoyed by anyone who likes flowers and/or gardening and/or seeing what sort of creations can be made from flowers. They have small signs up to tell you what kind of plants are growing or give little historical factoids, which is a nice touch. The biggest downside is that it can get a bit crowded/awkward with everyone running around trying to take pictures, but since it's free, I just come back at a less busy time to enjoy it again.