You'll see doors occasionally, on specific levels of specific dungeons. Behind these are treasures, items that power up certain types, or belong to legendary pokemon.
in dungeons sometimes the kelcleon shop in town same thing but cheaper dungeon-9000$-10000$ town-8000$
sometimes in dungeons you will find a door if you have a key you can open it the door sometimes the door opens to a rare Pokemon that can be recruited or a rare item
They don't open dungeons, they open locked rooms within dungeons. Certain unique items can be found, like the Silk items, and treasure items for Legendary pokemon.
just like on the red versoin if u defeat a Pokemon thay MAY want to join. ther is a item that will boost the liklyhood of Pokemon joining called the friendship ribbon it is only avalible with a key or cheating>
In Aegis Cave
in some dungeons there will be doors you use the key on the doors while facing them
Its on floor 30 of mount Faraway. you need a key.
in a key door on western cave B59F
they are on the floors of higher leveled dungeons.
You can find them lying around in Solar Cave.
you usually can find keys in the solar cave
go to mt.faraway and on floor 34 has a friend bow.bring a key to get it.