Neville Longbottom spent a lot of time on top of the astronomy tower throughout his years at Hogwarts. In his first year he went there to watch the school. People were nice enough to him, he guessed, but he didn't feel like he really belonged with any of the guys in his year. Harry had Ron. Dean had Seamus. The rest were in different houses, leaving Neville with nobody. From the top of the tower he could watch the rest of the students and pretend he was one of them.
In Neville's second year he would climb the tower to do his homework. He wished he had someone he could ask for help, but he still felt isolated from his classmates. The tower offered him a place to work and practice without feeling self-conscious. Here he could avoid the laughter and peer pressure he struggled with in the Common Room and the Library. Neville wanted to be as good of a wizard as his dad had been, to make his grandmother proud.
Neville spent his third and fourth years in much the same way. His diligence would have easily earned him a place in Ravenclaw. He studied more than almost any other Hogwarts student, but he still struggled. Some days he would sit at the top of the tower from the moment classes ended until after midnight. No one really knew what he was doing up there and unfortunately not one single person bothered to ask him.
Fifth year brought O.W.L.s. As if Neville didn't struggle enough as it was. The astronomy tower became his safe haven. When everything he had to learn and do began to overwhelm him, he would leave everything where it was and climb the tower. Here Neville could rage in frustration or cry in his desperation without fear of judgment. This is where Luna found him, one unusually warm November day. Neville had been crying but now he sat against the wall of the tower. He knew his face still bore the evidence of tears but he didn't bother to try to wipe them away. To Luna's credit she didn't say anything, she simply sat down beside Neville. He realized he actually enjoyed Luna's company. It helped him to calm down. They spent a lot of time sitting on top of the tower that year, usually just sitting.
Luna and Neville didn't really talk until their sixth year. Now when they met at the top of the tower, they would talk about whatever circumstances had led them there. Neville found that this helped more than anything else could have. Luna listened and responded without malice or judgment and often had simple, beautiful advice which Neville followed to the letter.
Seventh year was harder. With Professor Snape in charge it was harder to get to the astronomy tower and back without getting caught and punished but the two outcasts still managed. They would sit and watch the stars as they arched across the inky night sky. When Luna was taken by Lord Voldemort, Neville continued to climb the tower and talk to the wind as if Luna could be there to hear his problems and give him her wonderful advice.
The day of the Battle of Hogwarts, the tower fell. Neville watched it and he felt a part of him die. All the memories that had been made there were done. There was nothing left but to wait for them to fade with age. That was when Neville realized, that tower was someplace special, and it always would be.