Lake Mashu ("Mashuu-ko" in Japanese) is a freshwater caldera lake located about 50 km south-southeast of Abashiri and about 70 km north of Kushiro. It is one of the three lakes in Akan National Park. It vies for the position of "clearest lake in the world" because of its remarkable water clarity and heavy mist which shrouds it.
The lake is also considered by many as the Japan's most beautiful lake and one of Japan's deepest lakes.
Visitors are not allowed to go down into the lake but it has two observation decks around the rim of the caldera that visitors can enjoy the view. Observation Deck Number 3 that lies along the western rim of the caldera that consist of two decks with views of the lake and Mount Mashudake.
A 5 minute drive to the south is the Observation Deck Number 1. It has multiple viewing decks, toilets and a large shopping area.
Visitors may also go to Mount Mashudake on the western part of the lake which has a hiking trail that offers an even more beautiful angle of the lake.
The public transportation varies every couple of months.
From April to early July, the buses run only between Mashu Station and Lake Mashu's observation deck number one, while from mid July to October, the connection from a bus ride vary with different stations or landmarks.
During the other months (January, February, March, November, and December), no bus service can connect you to the lake.
The lake is open to the public anytime. No entrance fee. The only expense in travelling in this place is the transportation and the parking fee (if ever you will bring your own car) in the Observation Deck Number 1 which cost 410 yen.