Four volcanic rocks known as Colibrí, Terreras, Horadada and Bergantín form the most prominent part of a group of islands known as the Columbretes, which are located 34 miles from Castellon. The first of them, which is also the largest, is known as Grossa Island and occupies an area of ​​just 10 hectares. It is the visible part of a volcanic cone formed by two hills, joined by a rocky tongue strewn with lava and slag, in which just a few nopales and low scrub grow. It forms a natural bay open to the east known as Puerto Tofiño, which is very dangerous due to the strong Levante wind. The island has an average length from north to south of about 900 metres, and a maximum width of 200 metres.

The highest hill is the one in the north, which is 65 metres above sea level. A lighthouse was built on the summit and was considered the worst destination in the entire Iberian Peninsula for a lighthouse keeper to be sent because it was so isolated. The southern hill is 45 metres high and has a small cemetery with eleven graves, a funereal memory of the lives of lighthouse keepers and relatives condemned to such a painful exile, and a monument to the Sacred Heart.

These islands were cited by Pliny, Mela and Strabo under the name of the Serpentarias, and were included by the Greeks in the group of the Ophiusas. These names and all their subsequent ones – Columbretes, Colibrí – are related to their ancestral inhabitants: snakes. Grossa was populated by the dangerous “vipera lataxi” viper, which was a serious problem that the inhabitants of the lighthouse had to deal with on an ongoing basis.

A squadron of death row inmates was first sent out to kill them, and they were granted a reprieve in exchange for their participation in the extermination. After several of them died, the method was changed and a herd of pigs, which eat snakes but are not killed by their venom, was brought to the island. Finally, around 1890, they disappeared for good.

However, the island was still not free of danger as scorpions replaced the snakes. This endemic species of the islands, much appreciated by naturalists, was part of the entertainment and fear of the keepers, who carried out nocturnal hunts to exterminate them. According to reports, there were times when more than 40 were killed.

Four entire families of staff members came to inhabit the lighthouse simultaneously. To ensure that there was always enough staff, it was necessary to hold an annual draw to provide the 1st and 2nd guards, with the other two being appointed directly. The fear of being chosen was so great that the head keeper of the Cabo Blanco lighthouse shot himself on 19 November 1869, when he was threatened with being transferred there.

The keepers spent practically all their time on the island without a break, as it was not until 1916 that shifts began, and even then, it was one month of rest for every three months spent on the island. Provisions arrived every fortnight, weather permitting, which was very rare in winter.

In addition to the aforementioned cemetery, a room in the old farmhouses was fitted out as a chapel dedicated to Our Lady of the Forsaken (Virgen de los Desamparados). As a curiosity, this is the inventory of the state materials existing in the chapel in 1915:

• 2 metal candlesticks
• 2 crystal chandeliers
• 4 glass vases
• 10 frames of different sizes
• 1 square of fish scale
• 1 box of verses to the virgin
• 2 benches
• 1 tablecloth for the altar
• 1 lamp
• 8 artificial bouquets
• 2 flower vases

The lighthouse began to be built in October 1856, under the direction of the engineer Mojados. The material to build it was transported on the steamship Destellos.

The lighthouse was brought into service on 30 December 1859, with a fixed white light and a range of 21 miles. It was equipped with a prismatic lantern and first-order device purchased from the French house Sautter at the cost of 66,316 pesetas. This device consisted of three zones and had 13 prisms in the upper one, 17 in the central one and six in the lower one. It also had a mechanical watchmaker’s lamp for olive oil, initially served by three keepers, equipped with a Dotty burner with four wicks which used olive oil and then moved onto paraffin and oil.

On 20 September 1915, the fixed light characteristic was changed to that of groups of three occultations every 20”, using the primitive device and a system of screens recovered from the Tarifa lighthouse mounted on a mercury float powered by a weight-powered clockwork machine. A Chance 85 was also fitted with Barbier tanks and a life-saving lamp from the same company with a constant level, a top tank and a five-wick lighter.

On 8 February 1938, the keeper was evicted and the lighthouse was occupied by the army, which took over and seized the transmitting station. At the end of the war, it was returned “together with a device to produce light”, in the port of Ferrol by the cruiser Canarias.

In 1956, three consecutive projects were carried out by the engineer Fernando Berenguer to automate the lighthouse. They included the acquisition of an acetylene incandescent device with a 50-litre burner, a solar valve, a 375-mm focal length lens to emit three flashes, and a new 3-metre diameter air-maritime lantern. There were plans to build a new tower, but in the end the existing lighthouse was used. Once the supplies had been ordered from the companies AGA and Racional, the automation works got underway, and it was brought into service on 24 July 1961. This removed the need for a keeper, once the correct functioning of the automatic light had been verified. For greater security and to ensure that the island would not be left without signalling in a hypothetical breakdown, two automatic beacons were also built at both ends of the island.

In 1984, a project was carried out to electrify it with solar panels, replacing the Dalen system and preserving the 375 mm catadioptric optics it had. It is equipped with a base electric drive and electronic control and automatic 4-lamp changer, 2 solar generators capable of producing 216.6 ah / d and 27 ah / d respectively, a set of 3,300 a / h and 330 a / h batteries, with the corresponding control devices, at a cost of 17,270,820 pesetas. Likewise, the damaged building was renovated and repaired.

Maintenance is carried out by a technician residing in Castellon, who was formerly stationed at the lighthouse, and makes periodic visits by boat. There are three different ways to get to the island depending on the sea conditions. These are simple stairways located at different points on the island. The most commonly used access is that of Puerto Tofiño.