It is located at Punta de n'Amer, the most prominent cape in the entire region, from which it dominates all the views. Despite its name, it is not a castle but a fortified tower, with a square plan, raised vertically at the corners and with sloping walls. It is surrounded by a moat, which contains a cistern, and access to the interior is through a drawbridge.
On the first floor, there are the chambers of the tower guards and a kitchen with a fireplace. A spiral staircase leads to the upper floor, which is not a solid structure but an attic or mezzanine supported by a framework. The same staircase leads to the terrace, which is all covered. The parapet has eight gun ports and four horizontal embrasures that allow the defense of the base of the walls, the moat, and the glacis.
The viceroy Lluís Vic already exposed in 1585 the need to build a tower at La Punta, but the University of Manacor (at that time Sant Llorenç was administratively part of Manacor) deemed it unnecessary because they couldn't afford the cost. Joan Binimelis, the designer of the coastal defense system of Mallorca, insisted on the need to build it, but in 1617 a new proposal from the Grand and General Council once again yielded no results.
It was not until 1693 that the project began. It was entrusted to the military engineer Martín Gil de Gaínza, and by 1696 the construction was completed. That same year, the first tower guards were appointed, receiving six muskets, six rifles, and two bronze cannons. A few years later, mounted troops were sent to the new fortress, and a flooring had to be prepared for their accommodation. In 1724, the gun carriages were rotten and had to be replaced; the drawbridge and the chimney also required repairs. In 1765, it was decided to build a cistern inside the moat because the tower guards had no storage system and had to fetch water from outside.
With the Conquest of Algeria in 1833, the maritime dangers had significantly decreased, and coastal surveillance was no longer a high priority. Bartomeu Bujosa and Francesc Fernàndez, the tower guards, were integrated into the new State Tower Guards Corps in 1852. That same year, the cannons were removed. In 1857, the army ceded it to the state, which auctioned it and it was acquired by Pere Orlandis i Despuig.
Although the threat that had led to its construction, Barbary piracy, had disappeared, the fortress remained a useful element for the defense of the coast against other types of enemies. Thus, during the Spanish Civil War and World War II, an observatory was installed in the fortress. In 1996, it was restored and turned into a museum.