Grand Exchange to Keldagrim
There is a trapdoor located in the north-western corner of the Grand Exchange, near the shortcut tunnel, which leads to the dwarven city of Keldagrim. The message when opening the Grand Exchange trapdoor says: This trapdoor leads to a small dwarven mine cart station. The mine cart will take you to Keldagrim.
Canifis to Mort'ton
There is a trapdoor located behind the Hair of the Dog tavern in Canifis which can be upgraded to a trapdoor shortcut to Mort'ton, placing the player near Cyreg Paddlehorn, by completing Temple Trekking. It is a reward for training Zachory Bragg to level 99, and can be activated or deactivated by using the Temple Trekking signpost near Paterdomus.