Mt. Snowfall (Japanese: ユキミやま Mt. Yukimi) is a place in Pokémon Channel. It can be accessed after buying the bus ticket from Shop 'N Squirtle.
Summary
There is the Ruins of Truth right of it and it can only be visited after 5 days of playing the game. At first when you arrive there, there will be a Gengar blocking your path so that you can't enter. You will need the Duskull Lamp to enter the Ruins of Truth. To get the Duskull Lamp, talk to Duskull on Springleaf Field.
The other features of Mt. Snowfall include the concert. The concert is performed by a Jigglypuff and a Kecleon. There are also igloos that Pikachu can look through. Also, Pikachu may build a snowman version of itself when it starts rolling a snowball around.