LEGO 6088 Robber's Retreat is a Castle set from 1998 valued at $250 for new and sealed sets, up 734% from an original retail price of $29.99. Annual appreciation has averaged 4.74% since release. On the used market, values range from $69 to $84 based on condition. Secondary market prices for new and sealed sets typically fall between $214 and $300.
LEGO 6088 Robber's Retreat is a Castle Ninja set released in 1998, containing 277 pieces and 4 minifigures. The lineup includes Kata the Robber Chief and two Black Ninja figures, with accessories such as multiple katanas and spears. The build is a three-story fortress featuring a large double-door entry, a sword stand with a hidden compartment, a booby-trapped katana beam, balconies, a functional catapult, and a removable modular prison cell. Unique elements include a green rope with handholds, a red harness, large black doors, and a red banner, and the modular sections are compatible with other Ninja sets; the set was also known as Robber Baron’s Stronghold.
A new and sealed Robber's Retreat is currently valued at around $250, with annual growth of approximately 3%, which is lower than other Ninja sets. The average used price is $70 for those in good overall condition. Based on current trends, this set could be valued near $262 within the next year. The 4 included minifigs account for approximately 19% of the set's total value.