Survey Island was one of the five islands of the Age of Riven. As with most of Riven's islands, access to Survey Island was restricted to Gehn and his closest followers. Compared to the other islands, the surface of Survey Island had been heavily transformed by Gehn for his purposes. The island could be divided into two main regions: a pair of ponds atop an artificial plateau, a larger pond atop a larger plateau, and a small cavern system underneath it all. Gehn's primary purpose with the island was to keep a detailed map of the five islands of Riven in order to track the Age's slow breakup, and also to surveil its inhabitants.
The Map Island
The surface of the island was heavily landscaped and bore little to no natural features. The lower plateau featured a shallow pond with large sharp rocks jutting out of the center at odd angles. The plateau was surrounded by over a hundred wahrk tusks. The purpose of these tusks was to intimidate the Rivenese who had a deep cultural fear of the large fish. For this reason, Gehn often added tusks and other wahrk imagery to areas that he wished to keep the Rivenese away from.
Situated further along the plateau was another pond that acted as a map of the Age of Riven as a whole. Five artificial mesas jutted up from the pond, each in the shape of one of Riven's five islands. The mesas contained shallow pools of water, which could be heated from below, and shaped into forms that roughly resembled the topography of the islands.
A fortress-like structure had been built long ago, which affronted a higher plateau. One of the five daggers of Riven was embedded in the top of the wall, causing a large crack to form. Though hadn't caused the dagger to appear, he took advantage of the situation by building an elevator inside the crack in the wall. Atop the higher plateau, accessible via the elevator, was a deep natural pond. Gehn kept several Wahrk pets in this pond. Along the surface of the pond was the island's firemarble dome, and a round floating structure called the map room. The map room contained a device which could display small segments each of Riven's islands using a Pin Art-like relief. The control panel for the map room could be found on a small catwalk that hung from the dagger, overlooking the lower plateau.
Beneath the plateaus was a separate underground complex. Underneath the lower plateau was a pool of water floating above a volcanic vent. At one time, this pool was open to the air, but Gehn had long since built over it. A small golden elevator could transport one through the pool and into the volcanic vent beneath.
The vent connected to a cave which led to a massive cavern that had a window into the upper plateau's pond. Here Gehn built a throne atop a large stalagmite, where he could watch the Wahrks in the lake, or surveil his subjects. Gehn's throne had a couple different viewing devices that allowed him to monitor Catherine in her cell on Prison Island, and the Rivenese at the lake on Jungle Island. He could also turn on and off a series of colored lights in the pond, which would summon his pet wahrks.
Gehn used equipment on this island to track Riven's slow breakup, and to keep an eye on his subjects living on Jungle Island. Two maglev tracks connected the island to its neighbors; one led to Jungle Island and the other to Book Assembly Island.