Ons lighthouse
On the 13 April 1865, the light of a 5º lighthouse, situated 22.5 metres from the northern point of the Isle of Ons, was turned on for the first time.

This was a 5º order catadioptrical light with a continuous white beam at a frequency of 2 second flashes. It had a range of 17 miles and an elevation of 128.4 metres above sea level. The tower consists of three sections, the lower two being circular and the top one octagonal . The first light was purchased from the manufacturers, Sautter, for a price of 10,746 pesetas and had an olive oil plunger. Thirteen years later, it was replaced with a Maris single-wick oil lamp.

Following the approval of the Lighting Reform Plan in 1902, it was decided that the light should have a greater range by means of three white flashes. In order to achieve this, as with many lighthouses, the tower needed reforms to increase the size of the building. The final solution was to build a new lighthouse on the base of the old one. The old tower was partially demolished and a new, octagonal shaped one with a 3.7 metre diameter lamp was built.

The new building was opened on the 4th July 1926 with a lens from the British manufacturers Chance Brothers mounted on a base and mercury floater with a capacity of 325 kg. The light consisted of an incandescent pressurised petroleum vapour system. The originally designed light was also changed for four lightning flashes every 24 seconds, with a nominal range of 24 miles.

In 1932, the outside of lighthouse was tiled and, together with the lighthouses on Sálvora and Sisargas, was one of the last pressurised petroleum lights to exist. In 1990, the feed system was changed to photovoltaic power.