Castle Walls is a Normal Trap Card.
Trap Cards are normally Set first and can be activated on a later turn, often in response to an action.
On the current TCG and OCG Forbidden & Limited lists tracked here, Castle Walls is Unlimited.
YGOPRODeck lists Castle Walls for these formats: GOAT, OCG GOAT, Duel Links, Common Charity, Edison, TCG, OCG, Master Duel.
A listed print of Castle Walls appears in Starter Deck 2006 (YSD-EN033) at Common rarity.
Among markets shown on this page, the lowest listed snapshot for Castle Walls is about $0.02 on Cardmarket (prices change frequently).
