It’s cool. One issue I have is that the colours for “Castle & château” and “Ruin” are very similar.

When you tap a marker often you can’t see the castle in the photo because it’s cropped to fit a rectangle with an unusual aspect ratio. That element should be allowed to adjust its height so the image is scaled at its own aspect ratio rather than cropped. Eg you can only see the mounds of Berwick Castle and Bamburgh Castle in the North East of England.

Also this one should be included: https://en.wikipedia.org/wiki/Caisteal_Maol