A cliff was a high, steep land feature.
Planet One had a cliff made of diamond. River Song graffitied a message for the Eleventh Doctor on the face of the cliff. (TV: The Pandorica Opens)
In Italy in 64, the Doctor's TARDIS materialised on a cliff, then fell off it. Neither it nor its crew was harmed. (TV: The Rescue, The Romans)
In Northumbria in 1066, the Doctor's TARDIS materialised on a beach near a cliff. The Monk observed this from the top of the cliff. (TV: The Time Meddler)
On the thirteenth moon of the thirteenth planet of the Thirteenth Galaxy in 1213, Bob Kreesus fell over a cliff when he slipped on a banana skin. (COMIC: Triskaidekaphobia)
In Cornwall in the late 17th century, the Doctor's TARDIS materialised in a cave near some cliffs. (TV: The Smugglers)
On Earth, the Doctor's TARDIS materialised on a cliff, then fell into the sea when part of the cliff broke off. However, from the perspectives of the First Doctor, John and Gillian, for whom time was in reverse, the TARDIS rose up out of the sea and the piece of cliff reattached itself. (COMIC: Time in Reverse)
On Oseidon, the Fourth Doctor and Sarah Jane Smith witnessed a soldier (actually a malfunctioning Kraal android) fall over a cliff. (TV: The Android Invasion)
In Cornwall in the 1970s, Romana I was lured to a cliff and pushed off it by Cessair of Diplos, who was disguised as the Fourth Doctor. She was rescued by the real Doctor and Amelia Rumford. (TV: The Stones of Blood)
Shortly after arriving on Dorsill, Peri Brown almost walked over a cliff, but was saved by Christopher Sheldon. (PROSE: Grave Matter)
On Dido in 2493, Bennett, disguised as Koquillion, threw Barbara Wright off a cliff. Bennett later fell off a cliff to his death while trying to get away from the two surviving Dido people. (TV: The Rescue)
In 2563, Bernice Summerfield fell off a cliff on Capella Four, breaking both legs. (PROSE: Walking to Babylon, Steal from the World)
On Peladon in 3885, the Third Doctor's TARDIS materialised on a cliff. The Doctor and Jo Grant exited safely, but the TARDIS tumbled off the cliff. However, King Peladon had some his men bring the TARDIS up to the citadel. (TV: The Curse of Peladon)
On one planet, the Doctor's TARDIS materialised at the foot of a cliff. It was then taken away by a giant lizard, forcing the First Doctor, John and Gillian to climb up the cliff. (COMIC: Lizardworld)
The Sisterhood of Karn forced Morbius off a cliff, presumably to his death. (TV: The Brain of Morbius)
While on Skaro, the Second Doctor pushed a Dalek posing as Omega off a cliff, destroying it. (TV: The Evil of the Daleks)
On Andromeda, Castrovalva was located on the top of a high cliff. (TV: Castrovalva)
On the Crooked World, the Doctor's TARDIS materialised on a cliff. It was later pushed off the cliff by the Whatchamacallit. (PROSE: The Crooked World)
In the Land of Fiction, the Master of the Land dwelt in a citadel on top of a high cliff. Jamie McCrimmon climbed the cliff with the aid of Rapunzel's hair. (TV: The Mind Robber)