Abstract: An underwater mobile observatory system comprising an aquarium (20) able to hold water and large enough to support fish, coral, and to display artificial objects such as shipwrecks and ruins, a vehicle track (21) extending through the aquarium (20), the track (21) generally being adjacent the bottom of the aquarium (20), the track (21) having a portion (24) which rises to a loading/unloading position, and a passenger vehicle (22) coupled to the track (21) for movement therealong and unable to leave the track (21) such that inclination of the track (21) causes the vehicle (22) to move up and down through water in the aquarium (20), the passenger vehicle (22) having a main body portion to seat passengers and which is capable of being submerged, and a top portion which is open to the air, the spacing between the track (21) and the water level being controlled such that water does not pass over the top portion.