Originally Posted by barnyb
Why not ask your wife if the two of them want to try it first and then you can join them at a later date.
I would've suggested this myself but the spa we know is abroad and so you can't just nip there at the drop of a hat. We tend to go when we're visiting the city. We've been to the city before with other, none work friends, but they've never wanted to go to the spa with us.
Thanks to everyone for your input and advices. On one hand, I think to myself it's only a bit of nudity. She'll have seen plenty of naked men before and so it shouldn't cause mature adults any sort of problem. On the other, she's a close work colleague who I get on very well with and there has to be a risk that it'd change the nature of the relationship and it seems a bit pointless jeopardising this.