So, just how do you pronounce Medieval?

[H.M.Stanley]

I once had a happy experience hunting for Belvoir Castle (think how the French might pronounce "Belvoir")

Only to be told be a yokel, sorry, local, "oh you mean Beaver (sic)!" Bloody peasants  

If you think about it, and feign a heavy dialect, you can see how we got from one to the other  

[Patrice]

"Belvoir" sounds easy to me 
It's probably Old French for beau-voir? if it's on a hill and you can see the landscape around.

Some years ago I worked in medieval Summer entertainments in La Hunaudaye Castle in Brittany. When friends re-enactors came from England to visit they had difficulty with the name, one of them called it "Castle Unpronouncible" 

[H.M.Stanley]

HM Stanley  

Belvoir Castle (pronounced Beaver) is a stately home in the English county of Leicestershire, overlooking the Vale of Belvoir (grid reference SK820337).

I know - i found it.

It has a nice ECW collection there. Or did have