I'm sure this is not a new thing, but I just found out about it, and I think it's pretty neat!
I had a lot of fun with that so when I was in Malaga. Sat in the beach for hours with a book, a bottle of chilled rose and grilled fish takeaway from a beach side restaurant.
Identifying all the boats that trundled by and their destinations was great fun. We even saw an unlisted navy vessel.