Pino-Roble de Canicosa de la Sierra
A Scots pine is growing out of the middle of an oak. Not beside it, not leaning on it: the pine germinated inside a hollow in the oak's trunk, most likely from a cone a squirrel carried in, and has grown up through it and out of the top. The pair is known as the Pino-Roble, the pine-oak. The host is a Pyrenean oak of about 250 years, 12.5 metres tall and 3.4 metres round. The guest is about 130 years old and has already overtaken it, reaching 15 metres. Its own trunk only clears the oak's crown at 2.9 metres up, which is where it was measured: two metres round. This is not a peaceful arrangement. As the pine thickens it splits the oak's bark and speeds up its decay, and the site that documents the pair records signs of decline in the oak and no conservation measures in place. You are looking at a slow takeover, halfway through. In 2016 the Pino-Roble represented Spain in European Tree of the Year and finished fifth among trees from fifteen countries. It stands in El Piquillo, an old dehesa of Pyrenean oaks at about 1,200 metres, on communal land. From the road toward Navaleno, a painted roadside rock marked Pino Roble shows where to park, and a path of about a kilometre leads to it. One hiker warns it is easy to walk straight past.
Paraje El Piquillo, beside the road (BU-V-8227) from Canicosa de la Sierra towards Navaleno, about 2km from the village then 1km on a marked path, Canicosa de la Sierra, Burgos province, Castilla y Leon You can recognise it by the pine trunk rising out of the top of a hollow oak, two trees sharing one base. It stands in the El Piquillo oak dehesa, about a kilometre's walk from the painted Pino Roble rock beside the road to Navaleno.
Free, on communal land beside a public road. lagunasdeneila.es gives turn-by-turn directions: take the BU-V-8227 towards Navaleno, about 2km out of the village there is a painted roadside rock marked 'Pino Roble' and a small dirt parking area, then roughly 1km on a marked path to the tree. canicosa.info independently confirms it stands right beside that same road with views back to the village. One source (tierrasdeburgos) calls it 'not especially signposted' and easy to walk past even with coordinates, which is a real caveat about how inconspicuous the pair looks against the surrounding forest, not an access restriction.
Rural Sierra de la Demanda, Burgos province; no public transport. About 60km from Burgos city and roughly 50km from Soria (neither currently published); realistically reached by car to the village and then the short walk described above.