(flavor text) How to (and best way) to put a message when the PC steps into a certain location?

So I am sure this is pretty simple... digging around the toolset for a feature but not sure where to look

All I want to do is send a message either in the dialog box, or could be above the PC's head... with some flavor text - IE, "you have entered what looks to be an ancient barracks, now in ruin"

What would be the nicest/best way (and how to) do this? thanks!!