Escape the Great Fire of London opens on May 21st, not sure what it exactly entails but always nice to see new stuff. Also, if you visit between 23rd and 27th May, and buy a Tavern Tankard, you will receive a limited edition pop badge.
https://www.thedungeons.com/london/en/explore-the-dungeon/escape-the-great-fire-of-london.aspx