The medieval English forest of the Robin Hood legend, recreated by Q in 2367 as a deadly game to test Picard's feelings for Vash.
Sherwood Forest is the setting of most of the Next Generation episode Qpid.
Wishing to repay a debt to Picard, and amused by the captain's awkwardness around the archaeologist Vash, Q transports the senior officers into his own version of the legend. Picard becomes Robin Hood, his officers are the Merry Men, and Vash is Maid Marian, held in Nottingham Castle and due to be executed.
Q takes the role of the Sheriff of Nottingham and makes it clear that the danger is real. Vash complicates matters by agreeing to marry Sir Guy of Gisbourne to save herself. Picard storms the castle with his crew, and Q returns everyone to the ship afterwards.