These are the areas around Hogwarts that still belong to the school. Not all of them are open for students, but most of them are accessible to students before curfew.
The Owlery
The Owlery was a room on the top of Hogwarts Castle's West Tower, where the school owls and the owls belonging to students lived during the school year. The Owlery was a circular stone room, rather cold and drafty, because none of the windows had glass in them. The lack of glass in the windows allowed the owls to come and go freely. The floor was entirely covered in straw, owl droppings, and the regurgitated skeletons of mice and voles. Many owls nestled here on perches that rose right up to the top of the tower. During the winter months, the room was very cold, to the point that one had to be careful with ice on the higher landings.
Path To Hogsmeade
This is the way from Hogswart to Hogsmeade. It is located on the edge of the Forbidden Forest and leads the the entrance of Hogsmeade.
Greenhouse
The greenhouses have statues of long, serpentine dragons running along the peaked roofs. They are home to many exotic and magical plants including some that are extremely rare, difficult to cultivate and maintain, or even dangerous, such as the Venomous Tentacula. Sometimes Herbology class is held here instead of the classroom inside.
Quidditch Pitch
Hogwarts has its own Quidditch pitch where Quidditch teams could practice, hold try-outs and play matches against each other. Each year will see a total of six inter-house matches (each house competing for the Quidditch Cup), along with numerous training sessions by each house team.
The Gamekeeper's Hut
The Gamekeeper's Hut serves as a home to the Gamekeeper (and some of his pets). It is a small wooden cabin located outside of Hogwarts Castle, on the edge of the Forbidden Forest. It is also used to keep certain animals such as chickens and ducks as food for certain magical creatures.
The Black Lake
The Black Lake (alternatively known as the Great Lake) is a large body of water located to the south of the castle. It is about half a mile in diameter and the Hogwarts plumbing network drains into it. It is home to a Giant Squid, Grindylows, and a colony of Merpeople. The Slytherin common room is beneath the lake, accessed through an entrance in the school dungeons. The Chamber of Secrets is also thought to be beneath the lake. Sea turtles can also be found within it.
The Forbidden Forest
The Forbidden Forest, also known as Dark Forest borders the edges of the Hogwarts School of Witchcraft and Wizardry grounds. As its name suggests, it is strictly off limits to students - except in the case of detention, or Care of Magical Creatures lessons that occasionally take place there. Of course, with the various dangerous creatures living in the Forest, few students would even want to venture into it. Black flowers are known to grow in the forest.
The Forgotten Grounds
The Forgotten Grounds was a closed-off area by the Quidditch pitch. It could only be acessed via an old, rusty gate that was kept locked; as a result, this area became abandoned and, gradually, virtually forgotten. It was enclosed by stone walls, although the far end had very thick trees that one could not cross. There were three areas there: a Puffapod patch; an area with an infestation of Horklumps, and an area with a fully grown Venomous Tentacula. Now it is used for Care of Magical Creatures class, since the overgrowth of Puffapods, Horklumps, and Venomous Tentacula create a perfect feeding and hiding spot of all kinds of magical creatures. Becareful of the Venomous Tentaculas thought; their bite is poisonous and may be fatal.