As for Archway Leisure centre in general:
I have been a few times, I always shower in the pool side where there are two sets of open showers. The open shower setup is actually great, although I think the potential of the centre is not exploited.
It's hit and miss, sometimes no one or clearly straight men, other times lots of looking and discrete hard-ons. Also, it's often full of families/schools. I try to go after 7pm or around 12pm, when it's adult-only, but it has happened that families have been around at unpredictable times. Weekends, the pool is full of families all day. Gym showers have cubicles, although I have heard sex happens sometimes in the gym locker room (smaller and more secluded).
The spa is not naked, everyone wears swimwear, but definitely there are men ready to get naked under the showers with you afterwards. Check out the squirt listing!
Hit me up to arrange a naked shower there!