Refers to the Hyrule Castle Dungeon. In Vanilla aLttP, Link used this route to escape from Hyrule Castle after rescuing Princess Zelda.
This portion of the game is often checked in Randomizer fairly early since it is accessible from the start of the game (albiet a bit difficult without a sword or some other way to attack) and contains three items. It’s also important to note that there is a second part of this dungeon commonly referred to as the Back of Escape, which is accessed through the Hyrule Castle Throne Room* or, more commonly, accessed via the pushable grave in the Graveyard.
*Please see Back of Escape for more information on requirements to access the items located there.