by Phlegm
One of the things that I really quite like are concrete constructions.
They're usually too big to take home, but they do tend to stick around quite well.
Where I live, there are dozens of them, randomly placed along the cliffs and higher ground.

The remains of these Yorkshire coast pillboxes were constructed for defence against enemy invasion during World War 2.
Spread around the country, they formed part of an 18,000+ strong force, built in 1940/41. Constructed mostly by the soldiers that would use them, they follow several different designs based on intended useage, location and available materials.

Decades of weather - wind, rain and salt air, have taken their toll on them, and many are in an advanced state of decay. Erosion of the cliffs here at Cayton bay, has caused many of the boxes to fall; some now laying upside down on the beach. These boxes receive a twice daily pounding from the North sea and all of them are slowly crumbling away.

I hope they'll be here for a few more years though, so children can play in them, as I did when I was a child.

And still do, now and then.