i belive that fromcenter you go down and there should be some hikers and ruin maniacs its around there their pokemon are about lvl 50-ish rock types to open the cave you use cut on the steel door hope this helps :)
Use HM cut on it.
It is located in Mt. Ember on Island One after you beat the Pokemon league. The cave that the rockets were blocking before is open for exploration after talking to Celio about the ruby and sapphire. After you get both, you can trade Pokemon Firered and Leafgreen to Ruby,Sapphire,Emerald,Colossuem and XD.
It's in Cinnabar island. It's where you get the key to open the Gym #7
You will find the key to the Gym of Cinnabar Island, From the Pokemon Mansion that is on the same island.
You need the secret key which is found in Pokemon mansion which is also on cinnibar island.
You need to Get a mystery gift
You need to know the move dive and get something from underwater
u need to skulk around the Pokemon mansion on cynnabar island for a key. its a bit of a hassle but you'll get it
You just have to go up to the door and have a Pokemon to use Cut on it. Simple. Hope that helps xx
Go to four island and go in icefall cave find HM7 in here which is waterfall use it to go up the waterfall in the cave go to the ladder then defeat the rocket then talk to lorelei go to six island and go to dotted hole the guy should be gone now use Cut on the door to open it.
You could find it in the dotted hole. Remember to bring a Pokemon that knows cut to open the door.
To open the rocket hideout, you need to get 2 codes. Lorelei will give you the 1st code in Icefall Cave. Then you go to Island 6 and go into the ruins. You will find a scientist who will tell you the 2nd code. Now go to the rocket hideout on Island 5 and beat up those miserable rockets.