The ruined medieval castle of Sant Joan sits on a rocky promontory at the north end of Blanes, above the botanical garden and the harbour. What remains is fragmentary — sections of wall, the bases of towers, and the outline of the original plan — but the location is commanding, with views down the coast south toward Barcelona and north into the rocky coves of the lower Costa Brava.
The castle dates from the eleventh century and was the seat of the Viscounts of Cabrera, who controlled much of this stretch of coast in the medieval period. It fell out of use as defensive technology made clifftop fortifications obsolete, and it has been a ruin since at least the eighteenth century. The walk up from the old town takes about twenty minutes; combine it with the Marimurtra garden next door.