Keep heading northeast on Route 7 past the Tower of Heaven to reach Mt. Negi. Make your way through this labyrinthine mountain to end up in Sekka City. Note: After your battle with Cheren at Mt. Negi, Adeku gives you HM03 – Surf. If you want to backtrack and explore around with Surf, feel free.
Items of interest:
As soon as you arrive in Sekka City you should be able to waltz into the gym and claim your badge.
Pokemon Daisuki Club
Not much here, but the woman in the house will tell you if your Pokemon is maxed out of EV points or not. The man will tell you at what level you caught a particular Pokemon and what level that Pokemon is now. Erm… yeah. He'll give you another Exp Share though.
The man standing to the right of the main desk in the Pokemon Center will buy your valuable items (nuggets, mushrooms etc) for double what the PokeMart pays.