I have to give a shout for France and Belgium. Countries where the cycle is respected and cyclists even more. But I live in the south east of England and have to give it a chance. Mountain biking up on the South Downs or North Downs if you are going to be based in London. The downs are chalk ridges that run across the south of England and there are several Offroad rides that are to be recommended. Living on the South downs- there is a Ride of 100 miles from Winchester to Eastbourmne taht involves 100 miles and 10,000ft of climbing. No hill is above 850ft but you start each one from sea level and grade can be as high as 20% in places. The ride can be done over 1-2 or 3 days. Relatively easy except for the one day ride but that is achievable for any "Super" human with a good 14hours to spare. I've attempted it 11 times now and only failed twice so it can't be that hard.
Report on one of my rides here
http://www.bikeforums.net/showthread...ns-Way-failure
But road riding and those Downs will offer a few challenges for the fit riders- or you can ride the valleys for flatter rides if wanted.
And Cyclists are getting a bit more respect over here so Don't rule out the UK- In particular down South.