Hi there clutz, I flew Lima-Cuzco back in May and spent a little time in the Caral lounge in the domestic terminal.

It's one of the smallest airline lounges I have used, and was crammed (not difficult!) when I first arrived. Happily most of the occupants all seemed destined for the same flight - but apparently not Cuzco - and once they had left, things were much quieter. The lounge itself was acceptable, but I only had about an hour to kill.

If there really IS a shower there (I had no reason to ask) then it's unlikely to be anything but a very basic facility.