SCUBA diving as a sport has enabled people to explore the magnificent ocean diversity of beautiful corals, striking fish, and mysterious wrecks. However, only a small number of people are able to experience these wonders as diving is expensive, mentally and physically challenging, needs a large time investment, and requires access to large bodies of water. Most existing SCUBA diving simulations in VR are limited to visual and aural displays. We propose a virtual reality system, Amphibian that provides an immersive SCUBA diving experience through a convenient terrestrial simulator. Users lie on their torso on a motion platform with their outstretched arms and legs placed in a suspended harness. Users receive visual and aural feedback through the Oculus Rift head-mounted display and a pair of headphones. Additionally, we simulate buoyancy, drag, and temperature changes through various sensors. Preliminary deployment shows that the system has potential to offer a high degree of presence in VR.