Cheap aquarium ideas that do not particularly include fish.?

I need ideas that don't cost much but are interesting and show nature's beauty hopefully. I have a couple empty aquariums that i want to do something with and not particularly the traditional fishtank because i already have one of those and its enough work. I was wondering if anyone had some ideas that are pretty cheap on the budget. Thanks. I did check on google but didn't really find what i was looking for and there's so much to read through.