Alright, I'll post this against my better judgment. Go to the basement of Snow Valley, on the second floor (best accessible from the alpha spawn with the tents). Go straight and to the left where you would exit. Run and jump behind the door.
If you made it, you will be behind the door. This works perfectly for Snow Valley. You have essentially glitched into the big tower thing. You can't be killed unless someone goes to the basement. You have clear shots at most spawns and the whole tower.
The down side is that you have to kill yourself to get out. I ran out of ammo and used my grenade. I was stuck for ten minutes before I convinced Bravo team to come kill me. Then I just did it again and saved my nade
But again, this is a useless spot without virtual jump.