The climb from the bridge too far up to water usually catches me out, and the last water-bar on the climb out of dingly-dell is a beast, by that stage you’re hanging and have to really heave yourself up and over.

Snowdon. Llanberis path. Just after the last but one station after the path goes under the bridge. The combination of the gradient and loose surface make this 50m stretch impossible for me. It’s the only thing that stops me from riding up in one go

The climb that links the bottom of Barry Knows Best and Pirch (TL then TR at bottom ie NOT thru P’lake)

Going back up skelghyll woods from Ambleside

Coopers Wood climb from Pilgrim’s Way/Exedown to the top of Wrotham Hill/A20. Never seen anyone actually clean it mainly due to the chalk/flints/ruts and the way it kicks up toward the top.

Even the local crosser-t*****rs struggle if it’s remotely damp.

Every part of this bastid.

Theres one near me which is a but fiddly, mostly because its narrow and tends to have a rut in the middle which has steepish sides and loose stones in the rut, so its easier (!) to ride on the sides. Plus it gets a bit steppy due to horseriders hammering it in the winter and there are lots of overhanging brambles to avoid. However it turns a corner, steepens and the rut deepens, to your already hammered legs are burning up and you have to keep a dead straight line to avoid pedal strikes, whilst trying to maintain traction.
Never cleared it, but I believe its possible with fresh legs (I tend to meet it at the end of a ride normally).