The spire has two sides-one in the Dry and one in the Watery. The Dry's end resembles a radio tower, and has a security checkpoint at its base. A scissor lift, a group of lockers containing oxygen tubes and masks, and a guard station are all found here.
At the border between the two worlds is a pulsing red orb that manages the gravity between them.
The Watery's Spire is a strange spiraling conical construction that peaks at the orb. It is presumed there is a similar security checkpoint at its base as well.
Some time later during the events of the film, the Spire was destroyed, causing the Watery to drain down into the Dry, and contact was resumed. As of the film's endpoint, the Spire remains in ruins.