And how hard is the 381k bit anyone who has done it before, is it lumpy?
The 3C was my first 600. I rode the first 300 to Castleford waaaaay too hard (I kept up with MSeries FOTP - 'nuff said).
There are long long sections of <1% average ascent, and some shorter periods of around 1%. Anything around the Leeds conurbation seems hilly to me - once you get East of Castleford, it's easy peasy to Pocklington. Then you cross The Wolds, which are fine - if you've cycled in Normandy, done PBP, ridden the Marlborough Downs, you'll know the drill - long wavelength rollers. More of the same after Bridlington, then something rather choppier when you interact with the Howardian Hills - there may even be a couple of chevrons. After Castleford, you're back in the Leeds conurbation, and at that time of night, the indigenous are a bigger issue than the hills TBH, but when I rode it, I fell apart at Castleford and needed a great deal of help and support from my fellow riders to carry on, so I don't remember much about this section apart from being hopelessly lost and homesick on yet another hill, next to the M62, feeling like hell. It's a great ride
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Day two is much hillier - but much more fun, I seem to recall.