What is most famous in Hokkaido?

sea food

Nature.

June is the best season to trek and/or explore world helitage, Shiretoko

http://whc.unesco.org/en/list/1193/multiple=1&unique_number=1370

Or, several more national parks are candidate to exercise. You may climb mountains, too if you like it.

Akan lake and Mt. Akan-dake and Mashu lake
Mt. Daisetsu-zan
Shikotsu and Toya lake and Mt. Showa Shnzan
Kushiro moor
Mt. Komagatake and lake Onuma
etc. etc and those places have also several Onsen hot spa resorts there.

For example, Nobori-Betsu Onsen is most famaous its own spa and bear farm, Ainu theme park. Jyozan-kei Onsen is very vonvenient location close to the city center of Sapporo and the airport.

Hokkaido's famous foods are many.

Ramen, seafood(Crab meat, salmon, scallop, sea-urchin aka UNI, selmon roe aka IKRA etc) and seafood Sushi, Mongolian style lamb or mutton BBQ aka Genghis Khan cooking or Jingisukan Ryori are popular ones there.

Ramen
http://image-search.yahoo.co.jp/search?ei=UTF-8&fr=top_ga1&p=%E6%9C%AD%E5%B9%8C%E3%83%A9%E3%83%BC%E3%83%A1%E3%83%B3

Seafood bowl
http://image-search.yahoo.co.jp/search?p=%E6%9C%AD%E5%B9%8C%E3%80%80%E6%B5%B7%E9%AE%AE%E4%B8%BC&ei=

Mongolian BBQ
http://image-search.yahoo.co.jp/search?p=%E6%9C%AD%E5%B9%8C+%E3%82%B8%E3%83%B3%E3%82%AE%E3%82%B9%E3%82%AB%E3%83%B3&ei=

Sapporo is big city. You can enjoy city life as same as Tokyo with much clean nature.

June is one of the best time to check out the flowers (ie. lavender) in Furano! In addition to Sapporo, other places you should visit is Otaru, Noboribetsu and Hakodate (these were my favorite when I went there a couple years back).

Furano - flowers and lavender-flavored ice-cream/soda/coffee/tea
Otaru - glass and music-boxes, coffee
Noboribetsu - the bear park!
Hakodate - fresh uni and fresh amaebi
Sapporo - ramen, cantaloupe, milk and milk chocolate and Sapporo-flavored (beer) everything including ice-cream, chips

Get a Japan Rail Pass and take the train around Hokkaido.

Is the winter festival in February or just food!!! lots of crab, lobster, meat, etc....

What Is Hokkaido Famous For

No one said GLAY! A famous J-Rock group who is from Hakodate, Hokkaido.

Besides that, Sapporo Beer is popular, it's from Sapporo, Hokkaido.

Nature, Ainu, there are a lot of famous things about Hokkaido. :)

But I think of Kubo Takuro, the guitarist for GLAY when I think about Hokkaido.

Ice cream is good in Hokkaido.
Since it's very cold/cool there, they use less water for ice cream, so taste so thick and yummy!

There is one Izakaya (Japanese style bar) called "I-ro-ha-ni-ho-he-to".
http://www.umai-iroha.jp/
It is GOOD!

Sea food is very poplular in Hokkaido too.

Lake Mashu is famous too.
But since most of the time it's foggy there, you are very lucky if you can see it.
http://en.wikipedia.org/wiki/Lake_Mashu

The night veiw of Hakodate is beautiful.
http://en.wikipedia.org/wiki/Hakodate

trees!
i have a picture of trees in hokkaido on my phone?