Where do I go next?

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I just beat the Veilstone Gym, and I am at the part where you can't get into the lake. Where do I go after beating the Gym?

[classy_cat18]

You go to Pastoria. Backtrack to Hearthome and go south.

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Thanks. The rival said that Pastoria was the next place he'd go, and I wasn't sure how to get to it.