Planet (Shark Bait)

An Earth-like planet had a barren and desolate surface. Its sea cast no reflections, had enough oxygen that it was breathable by non-aquatic life, and its bottom was several feet above the sea bed, from which it did cast reflections. It was home to bats, crabs, sharks, octopi, giant sea horses, a race of hat-wearing talking frogs, and the Ancient Mariner.

When the First Doctor, John and Gillian arrived on the planet, the TARDIS sank into the ground. They traced it to the bottom of an underground sea, where they found a group of frogs tying it up. After helping the frogs catch a shark that was trying to eat them, they celebrated by going sea horseback riding, but when they returned they found that the TARDIS had disappeared again. They traced it to a cave in which the Ancient Mariner was using it as his house, helped him build a new house, and departed. (COMIC: Shark Bait)