bathrooms
There are bathrooms on a number of different floors, but none in the common rooms or dormitories, apparently, since they had to be escorted to the bathroom when they were confined to their common rooms when the basilisk was attacking students. The Prefects and Captains of Quidditch have their own luxuious bathrooms.

Known bathrooms in Hogwarts:

• A boys' bathroom on the sixth floor becomes a battleground when Harry stumbles upon Draco, who is crying to Myrtle out of fear and self-pity. Harry hits Draco with a Sectumseptra curse, which lands him in weeks and weeks of detentions.
• Moaning Myrtle haunts a girls' bathroom on the second floor because it was here that she died when the basilisk came out of a secret entrance under a sink. The entrance led to the Chamber of Secrets.
• Hermione spent hours crying in a girls' bathroom after she overheard Ron saying that she was a nightmare, and that it was no wonder she didn't have any friends. A troll found its way into that same bathroom and demolished the place trying to kill her. Harry and Ron managed to knock the troll out and rescue Hermione, and the three became fast friends. There is no indication which floor this bathroom is on.
• The Prefects' Bathroom is on the fifth floor. [more...]
• The Room of Requirement appeared to Dumbledore early one morning when the Headmaster was walking along the seventh floor corridor with a full bladder. The Room was filled with chamberpots.

blackboard
Most classrooms have blackboards in them. Binns makes a habit of entering the room through his blackboard. Snape writes instructions for making potions on his with a flick of his wand.

Bloody Baron
The Slytherin ghost. No one knows why he's covered in blood, and no one dares ask. He doesn't seem to say much. For some reason, he is the only person who can control Peeves.

boats
A fleet of small boats takes first years across the Lake for their first view of the castle and their walk up the steps and in to the Entrance Hall to be sorted. Hagrid shepherds them through this process.

bookbags
Students typically carry bookbags filled with books, parchment, quills, and ink.

books
There are several types of books at Hogwarts. 

Library books
The library is filled with library books which are watched over by Madam Pince, who seems to treat students as thieves if they want to check a book out. Some of the books are rather nasty, especially those in the Restricted Section. 

School Books

recreational reading

breakfast

broom cupboard
 

broomshed
Located near the Quidditch pitch, the broomshed is where the school brooms are kept. Harry didn't keep his Firebolt there.

broomsticks - rules concerning

building materials
The walls of the castle are made of thick stone. The front doors are made of oak. In the dungeons, torches are set into the walls at intervals. The castle is draughty and cold during the winter months. Some of the windows are broken or cracked. Tha main staircase is made of marble.

buildings
Besides the castle itself, a number of buildings can be found on the Hogwarts grounds. These include:

• Hagrid's hut
• greenhouses
• Quidditch buildings, part of the Quidditch pitch, including the clubhouse with dressing rooms and the broomshed
• gates - the gates are flanked by stone pillars with winged boars on top of them