Castles in the Sea

Maud and Mishka Petersham seemed to like a certain stylized kind of castle and waves that I like too.  These are all from Tales of Enchantment from Spain (1920) .

Here is an intial:

Here is an arch leading to one:

And here is a big color pic.  Unfortunately the scan of the book isn't too good.  I'm sure it would look better in person:

In the book these are called a castle in one instance and a palace in another.  They seem to me like ornate towers and I imagine they might hop from place to place magically.