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https://www.solsticesprint.com/
Met a guy doing this on holiday, 1000Km endurance race where you only have to ride pre defined climbs, the rest of the route is for you to design.
It sounded like a great test of riding endurance and route planning, no idea things like this existed.
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Long days mean long rides. The Solstice Sprint is a 1000KM ‘checkpoints up front’ ultradistance bicycle race around the UK, starting and ending in Warwick(UK), set on the summer solstice. Riders must visit 10 checkpoints in order of 1-10, each checkpoint has a mandatory parcour, how riders get to each checkpoint is up to them.
The first edition of the race is focussed on the Midlands, South and South-West, riders will visit unbelievably scenic areas such as the Chilterns, Exmoor, the Malvern Hills, Mendip Hills(Cheddar Gorge). Riders will also tackle some of the UK’s most challenging climbs including Challacombe Hill, Gospal Pass and Porlock Hill."
There's something similar called All Points North which is a long weekend ride starting/finishing in Sheffield.
The 10 checkpoints are published in advance, it's up to each entrant to work out their own route between each one but they can be visited in any order. Only rule is that you visit them all and arrive back in Sheffield before the cut off.
Oh and that you obviously do it all under your own power/unsupported etc.
That usually works out at about 1000km as well.