Whomping Willows attack anyone and anything that comes within range of its branches. This particular Whomping Willow was planted to disguise the opening of a secret passage leading from the Hogwarts grounds to the Shrieking Shack in the village of Hogsmeade. Not many students know of this passage.
Press the secret spot on the tree, and he will freeze and let you pass. Just make sure you don't get hit.

"Hundreds of seats were raised in stands around the pitch so the spectators were high enough to see what was going on. At either end of the pitch were golden poles with hoops on the end."
Welcome at Hogwarts' Quidditch pitch! Here, you can practice, alone or with your house team, or just come and cheer for your favourite team in a match.
Flying lessons for first years also take place here.

In this little cabin, Hagrid still resides. It is small, and cosy, and stands at the edge of the forest, next to a pumpkin field. When in troubles, Hagrid will always be there for his favourite students. He's not teaching any more though.

This pretty lake on the South of the Hogwarts ground dominates the grounds. It is large, and cold in the winter, though you can swim in it in summer. The water is calming and the rocks at the edge of the lake are magnificent. Next to the lake, there is a gorgeous willow three to relax under.
All together, this might be one of Hogwarts' most beautiful places.

The Hogwarts' grounds themselves. Grass, trees, flowers in summer, snow in winter... What more do you need? The gate to Hogsmeade can also be found here. For the rest, there is peace and beauty.