Arenaceous means made of sandstone.
It can be a cliff:
photo by portengaround
or a work of art:
Qtub: photo by ampersandyslexia https://www.flickr.com/photos/88916555@N00
or a building:
this is Sandstone School in Sandstone, Minnesota, USA. I assume this is made of sandstone.
Arenaceous can also describe a plant which grows most happily in sandy soil, so this this might be the easiest spot for you if you have sand dunes, a desert, or an old building site near you - or, indeed, if you know someone who has a cactus as a houseplant:
And what's all that got to do with arenas?
Spot the Frippet: something arenaceous. This word comes from the Latin word harēnāceus, sandy, from harēna, sand. The first arenas had sand sprinkled on the floor before combats.