Actually the doors are there at every five lvls I believe, and at lvl 10, I got a Waterfall HM. Anyway, just keep trying to open doors there, you'll find it eventually. Also you can get evolution items in there, including Link Cables for pokemon like Haunter ---> Gengar, etc.
Revan is one of the greatest Jedi of all time. Danzx made this Sig and Avy for me