Adds a new game menu option "Show known Landmarks", which presents a list of landmarks (up/down stairs, golden chests, zone entrances and the like) that you've seen on the current level and allows you to go to them or view them on the map.  You can also set your own landmarks for later reference by right-clicking on the map and choosing "Set landmark".

Also available as part of the ZOmnibus Addon Pack and ZOmnibus Lite.