Yes there are showers down by the toilets (actually I think just one shower) but (at least last April) there was a supplementary charge - 30 euro from memory - to use them (at least for me, accessing extime with a BA boarding pass, not sure about others). I was in quite early and the shower was actually unlocked and only found about the charge when I asked for a towel at the desk. I didnt see anything stopping you just pleading ignorance and wandering in to use it as long as you had your own towel!.