The Tiny Mouse's House (アリネズミの里, Arinezumi no Sato, lit. Tiny Mouse Village) is an event in Tomba! 2: The Evil Swine Return.
To activate the event, simply walk towards a Tiny Mouse's House, for example in the Town of the Fishermen. Now you have to progress through half of the game to reach the Water Temple.
After you have talked to the man below the who wants the three Cogs from earlier events in the game, go and fetch them and bring them back to him. Watch the cutscene and then go through the tunnel to become small. It is recommended to go through the door at the end of the Minitta tunnel in the Water Temple, as you will get a Minitta Bell from the mouse who lives there.
Use Magic Wings or Baron to travel back to the Town of the Fisherman and go through the door to clear the event.