There is no many people who do not like to watch aquariums and who do not feel relaxing while doing that. Colorful exotic fishes are surely beautiful and attractive but they are not so exotic without adequately environment.
Here you can see some really interesting and unusual aquarium designs.
Here you can see some kind of aquarium labyrinth which is made of few of glass bubbles which are connected with water-filled tubes so fishes can travel from one bubble to another. This aquarium is really one of those which will attract the most of sympathy of your guests.