That depends on your version...
In Ruby, it's in a cave to the East (right) of Lilycove City, which you can only access after confronting Team Magma at Mt. Pyre.
In Emerald, the Team Magma Hideout is on the Jagged pass between Lavaridge City and the summit of Mt. Chimney. The entrance will not appear until you confront Team Aqua and Team Magma at Mt. Pyre, where Mt. Pyre's matron will give you the Magma Emblem, telling you that a member of Team Magma dropped it and that it must be a key of some kind.
near team aquas hideout in sapphire. but in emerald it is on MT. chimeny
Team Magma/Aqua's hideout is east of Lilycove City. You have to surf north from the beach to get there.
Is near mt chimany for team magma and team aqua is in lylicove city near the shore
First of all that's not magma's hideout someone drew on the sign Team magma rules! Use the move secret power on the tree to make vines appear.
Mossdeep city here is how you get there. Beat team magma in their hideout and beat team aqua in their hideout to gain entry to mossedeep city. Mossedeep city is right of lilycove city
The Magma Base doesn't exist in Sapphire Version, but the team Aqua's Base is located outside of Lilycove City.
There is no magma amulet in ruby. The location in which team magma's hideout is actually is the place where team aqua's hideout is in sapphire and emerald (i think you confused sapphire with emerald)
Team Magma`s hideout is where you go down from the cable car east of lavaridge. Team Aqua`s hideout is on the East side of lilycove, you surf northeast to get there.
The cove at lilycove city (i think it closes after you beat team magma) the masterball is inside there too =) so make sure to get it and then head out =)
the hideout of magma/aqua is just north of lilycove but you must use surf from the east
team magma's hideout is in lilycove city go to the magma's grunt that train a wailmer surf up and see for a cave ., if there are no entrance go to the slateport and talk to capt. stern that has an interview , after that he escort you to inside then go , after that go again to the magma's cave and now there you go .
There is no bases I think It is behind Lilycove city go east then north and you will find a hideout of magma.