Wormhole-jumping

Wormhole-jumping was an extreme sport that visitors to the Martian Lunar Park on Phobos participated in. It involved jumping into a wormhole found at the top of a snowy mountain. A gravitational anomaly prevented jumpers from touching the sides of the wormhole. Because of the hole's seemingly infinite depth, participants would make the jump with a bungee rope so that they could be pulled back up.

Hayd once managed to wormhole-jump to a depth of three kilometres. The Eighth Doctor wormhole-jumped on Phobos to communicate with the Entity of Fear, a god from another reality who had created the wormhole when trying to bridge from its reality into N-Space. (AUDIO: Phobos)