Eiffel, Eifel or Yr Eifl

What do these three places have in common?

(1)

(2)

(3)

                           
Surprisingly, it's the name. 
(1) is Yr Eifl, a mountain with three summits on the Llŷn Peninsula in Gwynedd, N.W. Wales. 
(2) is the Eiffel Tower in Paris.
(3) is the Eifel mountain range in western Germany and eastern Belgium.

(2) and (3) are connected by one man, Gustav Eiffel (the engineer who built the Eiffel Tower). His family had moved to France at the beginning of the 18th century and they changed their surname soon after from Bonickhausen to Eiffel in honour of their homeland.

(1) and (3) are original place names. 
To these we can add (4) Péaule, a commune in the Morbihan Department in Brittany.

The historic names of Péaule are Plebs Gablah, 878; Plebs Gavele, 1008; and Ploeaule, 1454. These are interesting because they reveal its origin in Old Breton: gabl/gavl, ‘fork’, ‘angle’, ‘corner’. 

This neatly describes its position on the coast at the intersection of routes from Vannes to Nantes, Redon and Rennes.

(1) Yr Eifl comes from the Welsh: gafl/geifl, 'fork/s' where the 'g' is lost by mutation. The three summits clearly explain the origin of this name.

This only leaves (3) Eifel. 

Although there have been attempts to derive this name from earlier Germanic forms, these have been unsuccessful. 

Perhaps it's time to try a Celtic origin (there was a Celtic presence here). 
After all, in such a volcanic landscape it is qúite possible to see forks, angles and corners almost everywhere.