What's a fluvarium? Well, in the case of St. John's, it's sort of like an upside-down aquarium. This low, octagonal structure at the edge of Long Pond -- near Memorial University, a few miles west of the downtown -- opened in 1990 to explain local freshwater ecology to kids (and tourists). The facility actually flows three stories down into the earth, just like water. The second level features exhibits on river ecology, including the fascinating marine life in stream riffles (where trout spawn) and shallow pools (which are rich with nutrients). On the lowest level, you look back up into the deep pool standing alongside the building; watch for big brown trout swimming by. These trout swam here naturally, of their own volition: a fish ladder leads to and from the museum to a local river, pond, and eventually the ocean. Pretty cool. Plan to spend an hour with the kids if you're in this neighborhood.