Are all spas co-ed? Will members of the opposite sex be sharing facilities?
Most spas are coed but all have separate facilities for men and women (locker rooms and showers, specifically). However, it is likely that you will encounter the other gender in common areas such as rest areas, dining areas, reception, patios, etc. Some spas are same-sex only, or reserve certain days of the week or times of day for each gender. Check with your intended spa for their specific practice.