Cutting back very overgrown climbing hydrangea

I have a very large overgrown climbing hydrangea. It's planted against a fence and is about five feet thick. It looks beautiful but has completely overgrown the border beneath.

I'm thinking of cutting it back hard to take it back to being a normal climber width (about 1 foot?) and thinking now as it's gone / going into dormancy would be a good time.

Wondering if anyone has any experience of reducing one in this way and if there is anything I should be aware of before doing it.

Thanks in advance for any replies.