You have to get out of the temple then and walk to the bridge and look for the balloon.
If I remember correctly, exit the altar room and see the large pool at main area. The exit out of the temple is right of that pool.
From the walkthrough:
Go back to the temple landing outside, down the stairs, bridge and before the next bridge meet Angela Davis' ghost. She says that you should go to Matia's Zone, new coordinates to get there, rituals abound, calculations might be key to heaven and possibility to get off the world. Dr. Hovis comes out to say his own warnings. Cross bridge, cross metal bridge, tunnel gate, left, forward, right, forward to cross the metal ramp, up the elevator by clicking the lever on the pole on the right, cross bridge, pan right and forward up the stairs to the fish balloon. Go to the chair with the steering mechanism that has icons - the one to the right. Click leftmost lit button at bottom left of screen and then click the round button at the center of the steering mechanism.