Siralos

Siralos is a planet composed purely of psychic energy. It is also said to be one of the seven hundred wonders of the universe. In the CD-ROM game Destiny of the Doctors, The Master uses the power of Siralos to trap the first seven incarnations of The Doctor in a series of traps, one Doctor per trap. Also, The Master entraps members of several of the Doctor's enemies such as Daleks, Sontarrans, and Cybermen. He creates a series of dungeons and deathtraps for his amusement.

The Doctor's servitor device, known as The Graak, is tasked with rescuing each of the seven Doctors from the Master's deathtraps. The Doctor's TARDIS as well as the Master's have both been entuned with Siralos so that the Graak may reach one of the Master's dungeons by crossing The Great Divide, a nexus which leads either directly into the psychic energy of Siralos, or into one of its manifestations.

The Master assigns various missions to the Graak during his quest to rescue the Doctors. These usually take the form of riddles or retrieval of an item at the Master's request. Upon sucessful completion of the mission, is the opening of another portal across the Great Divide. This takes the Graak to a more physcial, action oriented scenario. One such scenario has the Graak materialize within the Doctor's own brain. Another has the Graak engage in a space battle with a Dalek ship. Other scenarios include car and train chases, jousts with Sontarans, and various other mazes. Upon the successful completion of these scenarios, the Doctor of that level is released from capture.

Trivia
Siralos happens to be an anagram of Solaris. Solaris is a novel written by Stanislaw Lem. the planet Solaris is also a planet which causes illusions based on the thoughts or living beings that are close to it.