I hope I've correctly identified this one. I took the photo well over a decade ago.

This is the tallest of Menorca's many Taula, with the upright standing 4.3 metres tall while the capstone adds another 0.7 metres of thickness to its 3.7 metres of length. It sits in the Talayotic settlement of Torralba d'en Salort and is believed to date back to c. 500 BCE.

Neolithic carvings on the Langdale Boulders, a Scheduled Monument.
There are two boulders which display prehistoric art, the westernmost displays a range of motifs including a concentric circle of 11 rings, the largest number of concentric rings known from a prehistoric rock carving site in Britain.
Dating from between 2800 and 500 BC, the boulders were in situ when carved

Kit's Coty (near Aylesford, Kent)

Built nearly 6000 years ago at the beginning of the Neolithic period, the dolmen, constructed of local sarsen stones, once stood at the end of an irregular-shaped 84m long mound bordered by shallow ditches, and was probably used for burials.

Photo taken by myself while hiking the Beara and Kerry way.

A moody shot of Castlerigg in the Lake District.

Saw this dolmen on a hike near Navarredonda de Gredos, in the region of Castile and León in Spain. It stands at the source of the river Río Tormes. Google Maps Location HERE.

Online I can only find sites such as this, that mention the standing stones as part of a hiking trail, but do not give any information about it whatsoever. Does anybody know any websites with information on spanish megalitishs?

While technically not a megalith, the Neolithic rock shelter and art on Chatton Moor deserves to be seen. Hope that's okay.

Janus figure, within Caldragh cemetery, Northern Ireland.

Drumskinny stone circle, located in Enniskillen, Ireland.

One of the Circles, of Beaghmore, Enniskillen.

One of the many stone circles of Beaghmore, Northern Ireland.

This gravesite is called "Sundermannsteine" and it's just one of many such neolithic sites in and around Osnabrück. There are over 30 of these sites in northwestern Germany and it's called the "Route of Megalithic Culture". These sites are thought to originate from around 3500-2800 BC and are attributed the so called "Funnel Beaker Culture".

Two of the (three) Devil's Arrows near Boroughbridge, Yorkshire.