Moaning Myrtle’s bathroom, the stone gargoyle entrance to the Headmaster/Headmistress’ office, the Defense Against the Dark Arts professor’s office are a few places that can be found on the second floor of Hogwarts.
Moaning Myrtle's bathroom, a girls' bathroom, is located on the second floor, but it is out or order since she haunts it.
There is an empty corridor with a stone gargoyle that is the entrance to the Headmaster/Headmistress' office
Harry tore up the stone steps, through the oak front doors, and off up the marble staircase, toward the second floor.
Five minutes later he was hurtling toward a stone gargoyle standing halfway along an empty corridor (GF28)
This presented a question of how Dumbledore that year could have wound up in the Room of Requirement early in the morning when in urgent need of a bathroom, since the Room of Requirement was on the seventh floor in Harry's fifth and sixth years. In book 6 the entrance to the Headmaster's office was relocated to the seventh floor.
Defense Against the Dark Arts professor's office:
The windows of the office face south toward the lake (GF, Moody looked out and saw Durmstrang ship) and also west toward the Quidditch pitch (OP13)
The office changes hands every year, so the decor is different every time.
- Quirrell - unknown 1991-1992
- Lockhart - vanity pictures of himself 1992-1993
- Lupin - grindylow tank and other creatures for use in class, tea things 1993-1994
- Moody - Foe-Glass, Dark Detectors, seven-lock chest 1994-5
- Umbridge - plates on the wall with foul kittens in bright colors, frilly doilies and the like, flowered tablecloth 1995-6
"Saturday afternoon seemed to melt away, and in what seemed like no time, it was five minutes to eight, and Harry was dragging his feet along the second-floor corridor to Lockhart's office. He gritted his teeth and knocked." (CS6)
Note: there is a suit or armor near the office.
In Harry's second year, he serves detention with the annoying Gilderoy Lockhart in his second-floor office. From there, he leaves and hears the Basilisk in the walls and runs all along the second floor to listen to it.
After Sirius Black breaks into the Gryffindor Common Room, the Fat Lady is found hiding in a map of Argyllshire on the second floor.