Instructions
Complete the Summer's End quest to gain the ability to travel to the Spirit World.
Obtain a new Jennica's Ring if you lost the one you earned in the previous quest. To find a new ring, search the rubble pile north of Varrock.
Find a way into the Rogues' Castle via one of several entrances. One way to gain entrance is to head to East Ardougne and then enter a house near the west wall. In the house, pull the lever to teleport to a wilderness area. Walk north and slash the spiderwebs with your knife. Continue northeast past the scorpion pit. From the pit, go southeast to find the Rogue's Castle entrance.
Head to the northern part of the ground floor of the castle to reach the jail cells.
Stand in front of the broom on the eastern wall next to the cells. Take three steps east from the broom.
Equip the Jennica's Ring to travel to the Spirit World. You become a ghost and can now pass through walls, doors and other solid objects.
Walk through the first cell door, and then open the northern door. Go back through the first door and close it.
Deactivate Jennica's Ring to leave the Spirit World.
Walk through the open cell door to talk to the rogue.