Given that there isn't a whole lot to do in Liege and that I love biology, consider this review a…read morebit biased...
At first glance of this building, I couldn't believe it was an aquarium, since there are no outdoor tanks. I suppose it is a bit older style and attached to the Liege university, which is why. Nevertheless, we decided to check it out, as it was only about 7 euros to see the aquarium and museum (going to the sciences of the world section costs a bit extra).
The aquarium is downstairs and comprises about thirty or so tanks with fish from around the world - none too large though. You got your small sharks, turtles, colorful reef fish, lionfish, Dory/Nemos, and more. Some of the displays are a little bit difficult to read since it is rather dark down there, and the atmosphere is a bit humid due to being completely indoors, but no real complaints there.
Upstairs is the museum, where I thought things got pretty interesting. Although my brother was a bit grossed out at all of the specimens in formaldehyde, stuffed models, and skeletal forms, I was bio-nerding out at how cool everything was. It felt like a library of animals, and it was quite the extensive collection.
I thought the trip was a nice way to spend an hour, and it is different than the typical art/history museum experience attributed to Europe.