富士五湖, pronounced Fuji go-ko (Fuji five lakes), is famous for its lakes, for 青木ヶ原樹海 (Sea of Trees), and for its views of 富士山 (Mount Fuji). If you go there, you may also see monkeys in the mountains near 西湖 (lake Saiko).
Other places of interest in the area include 富士山 (Mount Fuji) itself.
A cheap and fast way to travel there from 東京 (Tokyo city) is by bus. Transportation from 新宿駅 (Shinjuku station) to 河口湖駅 (Kawaguchiko station) costs ¥1700, and lasts 1 hour 45 minutes. Tickets should be reserved.
Travel tips: Be careful in 鳴沢氷穴 (Narusawa cave), there is a slippery 90 cm high passage. You can also bring a headline to better see the stalactites in 富岳風穴 (Fugaku cave). Dinners at the café M, near 西湖 (lake Saiko), are excellent. The cottages at サニーデビレッジ (Sunnide village) are great and quite cheap.
Please check the photos of my visit in March 2007.