EXÍN Castillos, also known as EXIN Castles is a construction toy introduced in 1968 by the Exin Lines Bros., Barcelona.
The plastic blocks are of a peg-and-socket design similar to Lego, though with larger pegs and were designed for the construction of miniature castles. They are usually a mottled light tan color to resemble stone, and a few sets were made using pale blue blocks, for a castle "fantasy" theme.
Read more: Wikipedia
What's it worth? Take a look at this Exin Castillos price guide: sold listings for a value indication.