where is the cavern in pokemon emerald?!?

Question

i have finished emerald several times but now i have pokemon diamond i frogot everything about emeraldd,i've beaten the seventh gym and team magma at the station,got dive i went to sootopolis city but there's no groudon and kyogre fighting fighting and the 8th gym is still locked,i talked to steven he says there is a cavern between mossdeep and sootopolis where is it?!( i remeber what to do after i find kyogre and groudon fighting but how can i make them fight in sootopolis city?)

Answer 1

Here, they explain exactly how to get there.

Answer 2

if u stay above water and use max repels, it should be around route 227 i think it is..i dont really know, and u dive where the dark blue is. once u dive u must find it

Answer 3

its Underwater