There are three Runes or Bone Charms (don’t remember exactly which) inside the Dunwall Tower. One is inside the Lord Regent’s Bedchamber, the other in what I think is the Empress’ Bedchamber and one in a secret room near the latter. This guide explains how to get into it.
There is a video with a visual version of this guide below.
Dunwall Tower main mission: Opening the Regent’s Safe in the Dunwall Tower and Eliminating The Lord Regent Non-Lethally
My interest was captured when I used the heart and saw a Bone Charm behind what seemed to be a solid wall: