The "Berliner Höhenweg" is an alpine loop in Zillertal, Tirol, Austria. Due to the relative good infrastructure, but high difficulty (rugged rocks and mountains up to 3100m), the Berliner Höhenweg is one of the most desired FKT destinations in Austria for Trailrunners.

Start/End is Europahaus Mayrhofen. 

It is run anti-clockwise via the following Alpine Huts: Mayrhofen (633m) - Gamshütte (1921m) - Friesenberghaus (2498m) - Furtschaglhaus (2295m) - Berliner Hütte (2044m) - Greizer Hütte (2227m) - Kasseler Hütte (2278m) - Karl von Edel Hütte (2238m) - Mayrhofen (633m)

The Frankenwaldsteig is a 242km loop route in the Frankenwald of Bavaria.

John O'Groats to Land's End (JOGLE), or it's reverse route (Land's End to John O'Groats, LEJOG) connects the extreme tips of the island of Great Britain.  It's somewhere between 800 and 875 miles, depending on the route chosen.  The route has been done on foot and by other means at least since the 1870s, and records are kept for nearly every type of transportation imaginable including: 

This is a Premier Route. To claim an FKT on this route, you must meet a high standard of documentation and verification. See details here: https://fastestknowntime.com/premier-routes.

corsica.forhikers.com calls the GR20 "the toughest long distance trail in Europe". It runs about 180 km along the spine of Corsica.

Max Keith reported running this point-to-point route of 28km, with an elevation gain of 2800m, in 5h45m45s on 22 Dec. 2013. The route is just outside of Santiago, Chile, and begins at Ñilhue Bridge, Park Mahuida, and reaches the summits of Cerro Provincia, Tambor, San Ramon, and La Cruz. Keith appears to have had some support from a friend along the way. Here are is a report on the run, and a GPS track:

trailchile.cl/4-peaks-por-max-keith/