You likely know the place name even if you can’t pronounce it. Llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch in Wales has the longest name in the UK.
Did you know the longest single-word place name in England is Cottonshopeburnfoot in Northumberland? It’s just down the road from Blakehopeburnhaugh. Google maps will find them but I didn't see any signs in Street View.
In Scotland there's Coignafeuinternich.
There’s a list of odd and unusual place names, mostly in England, at www.ashton-under-lyne.com/placenames.htm/.