One of the things I really enjoy about living in Europe is the frequently encountered remains of relatively ancient structures, including forts and bastions.

I currently live 10 minutes by bike from a village that still has its star defense structures standing, and there's a nice walking path around part of it. - https://en.wikipedia.org/wiki/IJzendijke#/media/File:IJzendi...

There are also several towns in this country which still have impressive walls and gates. I still admire them when I see them.