My little girl is enamored with aquariums. She can watch fishes swim for hours. Once we could not enter a restaurant for a long time even though there was place available, because they had a large aquarium in the waiting area. She finally relented after much cajoling but dinner was interspersed with many breaks to see the fishes.
I have been toying with the idea of building an aquarium for her for some time and yes, I finally did it. I made this while Aanya was taking her nap, so it took me less than a couple hours. Here is a picture process of the same.