Help needed - Kitty safe 'arium

Ok, bit of a background but I'm a foster family of cats and got my own cats; they young once are about 2-3 kilo of weight and sometimes decides to zoom around like someone promised free kitty nip if they break the sound barrier and easily knock over items multiple times their weight.

As part of making their life more interesting I'm looking at creating a environment for them to look into (note I'm not decided on what type of animals to keep in it but unlikely to be fish but more on that later) to keep them entertained and stimulate them. Ideally active during the day (as we want our cats to sleep during the night) but not required. Hence I'm looking at setting up something with animals that move around (don't need to be anything to extreme speed but enough to cach the attention of a cat) that's very easily maintained and can with stand kitties walking/jumping on/off it. Obviously I don't want animals that would be afraid if a cat sticks their face up or paw the glass when it's on the other side.

In terms of size I'd like to keep it relatively small (ideally below 1m on any side) and avoid needing to be fixed to a wall if possible.

The only thing I've seen so far was a 50cm hanging ball of glass with frogs in it as example but I'm open for any ideas to be honest. I've had an aquarium as a youngster but nothing since (and those fishes tended to die a lot and reading this forum I did pretty much everything wrong but cela vie) of relevant experience.