It reminds me of a book that I adored as a young teen, about the history of Chester Zoo in the UK. Their very first polar bear was kept in an enclosure just like this picture with the tiny swimming pool. Apparently an old lady who adored the bear died and left a substantial amount of money to the zoo to do up a decent enclosure. The bear went for a swim in his new , very large and deep pool and for the first time ever he was white!
Is this one of the two enclosures by the beavers? The ring tailed lemurs are in one that looks like this, and one was covered by trees. I assume the sun bears use that at night like ZYBen mentioned above?