(And perhaps a few elswhere in the Isles)
Click on a letter in the top frame.
Tip: If you go to the Wikipedia link, you will often find a link like this:
Clicking on the given coordinates will take you to GeoHack - a utility
where you will be able to locate - via numerous options -
your castle on maps or aerial photos.
Suggestion: Scroll down to Global systems, and use the first one:
Find this location (Satellite, Hybrid) on Google Maps .