Meegat and Kim, did you get out of the Fractal Toilets of Taunton (surely related to the Roundabouts of Cumbernauld) okay?
Yep. After eventually resorting to some strategic use of the bushes, and a couple of hours dozing on a bench at a bus stop (turns out we were going for the full mini-audax experience), the railway station eventually opened. The first train back to Bristol turned out not to be crammed with cyclists as we feared it might so we got our bikes on with, well not ease exactly (real stroke of genius there by First, to have bike spaces that are too small to properly fit even our relatively small-framed steeds), but minimal difficulty.
My odometer ended up at 137km, of which about 112 was shared with Meegat, so she gets the metric if not the imperial century, and a decent introduction to night riding. Hopefully next year she'll have a bit more stamina for climbs, and I'll remember to bring my cycling lungs with me. Must remember to book that weather again - I did most of it in shorts and jersey without feeling cold until I stopped, and I quite like the option of functional braking while descending Cheddar Gorge.
The ride was excellent, and the big climbs aside, much flatter than I expected. The awesome moon and spooky (but surprisingly non-cold) mist just added to the atmosphere - IIRC Meegat's comment was "It's all gone a bit Playstation 1" as we passed through a particularly thick patch of it. As with everything, I reckon it would be a bit more fun as part of a decently sized slowish group.
The ranty letter to Taunton council about their general lack of toilet facilities, and overuse of recursive pointers to other closed toilets in explaining said lack, will have to wait until I've had some proper sleep.