Dark Barracks at Town Hall 15: max level 12. At Town Hall 18 the cap is level 13. It unlocks at Town Hall 7. Max level per Town Hall: TH7 2, TH8 4, TH9 6, TH10 7, TH11 8, TH12 9, TH13 10, TH14 11, TH15 12, TH16 13, TH17 13, TH18 13.
Tap a Town Hall to open this item there. Dashed: not available at that Town Hall yet.