Himalayas

The Himalayas was a mountain range in the middle of the continent of Asia on Earth.

Susan believed that Ian, Barbara, her grandfather and she had landed in the Himalayas when the TARDIS once abruptly malfunctioned. She called the Himalayas the "Roof of the World". Exploring, the party met Marco Polo, who told them that the year was 1289 and they were not in the Himalayas, but the Plain of Pamir, an area that he called the "Roof of the World". The TARDIS crew was invited to join him on his trek to Shang-Tu, the summer palace of Kublai Khan. (TV: Marco Polo)

In 1917, the Fifth Doctor took Erimem to Tibet for a legendary cricket match, only to unwittingly plunge her and Peri into a confrontation with the Great Old Ones. (AUDIO: The Roof of the World)

In 1935, the Second Doctor, Jamie and Victoria went to the Himalayas for a vacation at a Tibetan monastery, only to find the area had become overrun with real, living Yeti and robotic copies crafted by the Great Intelligence. (TV: The Abominable Snowmen)

In 2008, the Master (under the guise of Harold Saxon) sent the Torchwood Three team on a "wild goose-chase" to the Himalayas to prevent Jack Harkness contacting his team for help resisting the Master. (TV: The Sound of Drums) After the "wild goose-chase" the team apparently had no idea who had sent them there. Whether or not Jack told the team about the Master and what happened to them during the Year That Never Was is unknown.

Behind the scenes
"The Roof of the World" gives two different locations for the "Roof of the World". Susan maintains the Himalayas as the "Roof", while Marco Polo clearly states that the Plain of Pamir is. Though unexplained by the episode or the novelisation, they're both right. The Pamir Mountains are said to be at the intersection of the Himalayan, Tian Shan, Karakoram, Kunlun and Hindu Kush ranges. Thus, in a sense, Susan is right, but the "Plain of Pamir" is a more precise location.