Part 4: Beat Burgh — Castelia City Gym, badge 3

Beat Burgh — Castelia City Gym, badge 3 opens 3 areas.

Where to go

1. Desert Resort

   Wild: Sandile 40% · Lv 19-22, Darumaka 30% · Lv 19-20, Dwebble 10% · Lv 20-22, Maractus 10% · Lv 20 +2 more

2. Relic Castle

   Wild: Claydol 100% · Lv 47-50, Cofagrigus 50% · Lv 34-37, Krokorok 50% · Lv 34-37, Sandile 50% · Lv 19-22 +4 more

3. Route 4

   Wild: Frillish 100% · Lv 5-15, Alomomola 95% · Lv 5-20, Krabby 55% · Lv 35-55, Clamperl 40% · Lv 35-55 +9 more

Everything you can have caught by this checkpoint · Open the interactive guide

It also doesn't say when 4 of its areas open up, so they are listed together in the last part rather than guessed into the story.