The Elemen Mountains are a good place to train, however, a freak storm has blocked the path to three mountains: Mt. Blaze, Mt.Thunder, and Mt.Blizzard. The people who live nearby claim to unblock the paths you need three items that go onto nearby pedistals. Or, if you're not interested, you can stay on Mt. Terra, and train here.
(To climb Mt. Thunder, bring the shock orb.)
(To climb Mt. Blaze, bring the inferno orb.)
(To climb Mt. Blizzard, Bring the glacial orb.)
Or, travel here for pokemon encounters.