Sure, a Vivarium can be made from any Aquarium, all you need to do is lower the water level.
For a place for your above water critter(s) I would use those styrofoam shelves sold at Foster&Smith for reptiles. They will float, and the suction cups will attach to the side at the water line.
Common land Hermit Crabs are an excellent choice. I've had three of them and only one was stupid enough to think it could drag a sea snail shell that was four times too big for him from the floor to the surface.
Use some drift wood and/or rocks for a way to the critter(s) to get down and into the water and back out. Experts will warn you that any amount of water deeper than half the height of the crab WILL KILL IT.
Hogwash! They love the water, and love cruising along the bottom. These guys are herbivores and will eat algae like it is a gourmet food. Use the algae tabs for a small bottom feeder, and a fogger. The fog will carry the algae onto your airlines and electrical cords. You'll see them clinging to these as they clean them off.
Hermit Crabs are escape artists. I lost one this way, so, make sure there is no way for them to get out.
You can buy snail shells on line by the pound or piece, depending on the quality and type. Leaving a variety on the bottom for them to choose from, they will frequently change their shells, constantly looking for the right shape, size, color, or maybe like humans, for dressing up and going downtown, whatever.
My daughters friend gave me three of them that she didn't want after a week. They had "Peace at Any Cost - Surrender First" symbols and Dippie Hippie Flowers all over them. Eeek!
I ordered a few pounds of shells from an on-line supplier, and man the fun really began! They are seriously interesting creatures to behold. I kept them in what could be called a "Community Tank" because there was everything from cat fish, to snails, to guppies in the tank. On a smaller level, like a ten gallon, one or two of these with some feeder guppies, a rams horn snail or three, and a loach or two would make an excellent conversation piece that the kids would really enjoy!
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