Come back down from where Team Plasma is living and follow the road East to reach the Gym.  Hugh is waiting outside, and he’ll warn you that Clay is very tough- even having a bunch of Water-types to handle his Ground types won’t make things very easy.

The gym here is accessed by elevator, as the whole thing’s set into a mine.  A Fresh Water waits at the bottom of the first elevator, along with advice to bring in Water, Grass, and Ice attacks.

The gym is very dark, and consists of conveyor-belt chained platforms.  As you reach each platform, it will be lit up so that you can see the directions you’re allowed to go in, and any trainers waiting for you.  Follow the first conveyor to the North for your first battle.

Battle: Worker Noel (1240 Poke)
Opponent: Baltoy Lv 31

Take the East conveyor to the next platform, then head South, as the North conveyor is a dead end.  The South platform is also an elevator, that raises you so you can see where you’ve been and where you might need to go.  Use the conveyor to the East to get to another battle.

Battle: Worker Tavarius (1160 Poke)
Opponent: Drilbur Lv 29, Baltoy Lv 29, Sandile Lv 29

Head East twice, North once, and then West once to reach a third battle.

Battle: Worker Niel (1200 Poke)
Opponent: Baltoy Lv 30, Sandile Lv 30