Solo run of Halls of Reflection, the third dungeon in the Frozen Halls. It's located in Ice Crown and is meant for level 80 players. It can be summed up like this: Kill some dudes then run away from the Lich King while killing more dudes.
My brother is levelling another alt and has been doing some old dungeons and I've been joining in on occasion. This is our run of The Frozen Halls in Icecrown. We ran The Forge of Souls, The Pit of Saron, and The Halls of Reflection back to back. It's amazing how quickly and easily you can complete these dungeons when you're level 86-87. You should be able to solo all of these at 85.