I have developed a google maps overlay which shows all the National Trust properties, RSPB sites and English Heritage sites. This can be loaded into your google maps application so that, when you are travelling, you can see if there are any sites nearby that might be worth visiting.
It works better using the google maps app that it does through the browser.
Anyhow, if you think this might be useful you can click here to see the overlay and add it to your own version of maps. You may need to download it as a KML or KMZ file and then go to https://mymaps.google.com to import it.