Which entrance would you use?
The left entrance (the blue noren one) gives access to the men bathroom. The right one (the red noren one) gives access to the women bathroom.
Most onsen (hot springs) and sento (public baths) usually use the same noren colors and at the same time the sex is specified written on them, however if you can’t read Japanese this could be a problem.
Another possibility is that the baths are mixed (混浴 – こんよく: konyoku) in which women and men share the same ofuros. Although mixed baths are less and less common and you can only find them in very traditional ryokans.