Forbidden Valley Siege was a pre-alpha PvP Minigame. 4-8 players were able to side with Ninja or Pirates, 2-4 to a team, with the Ninja attacking a Pirate base to steal barrels, and the Pirates defending them. Three barrels would have to be stolen for the Ninjas to win the round, while the Pirates would have to defend for 5 minutes. The Pirates would have had thirty seconds to Quick Build defenses. If a barrel was dropped, it would have teleported back to the Pirate base after ten seconds on the ground. Players would have been able to build offensive and defensive structures such as walls, mines, bridges, turrets, bouncers, and gates, as well as being able to destroy the other team's structures. Players would have respawned five seconds after being smashed. The two placeholder team names were "Team Chuckles" and "Team Blockhead".
Forbidden Valley Siege would have been reskinned with a castle theme and released with the Kingdoms World as Capture the Princess. Although gameplay would have been exactly the same, the barrels would have been replaced by princesses and the Pirates and Ninjas would have been replaced by Lion and Dragon Knights.
A minimap for a similar test world, "Steve's Attack/Defend Test Map", was found in a beta client. This map was later shown in a video recorded by a LEGO Universe developer.
The map files for Forbidden Valley Siege are still present in the game data, and can be loaded.