"Womens" and "mens" are both meant to be irregular plural possessive nouns. There are different rules that cover singular and plural possessive situations.
First, if a noun is plural without adding an "s," the general rule is to add an apostrophe and then an "s." "Women" is already a plural noun, one that does not end in "s," so we follow this rule. The same is true for "men" and "children."
Second, if a noun is pluralized by adding "s," we place the apostrophe after the "s" to show possession. An example is "mothers." Here is a sentence to show you:
- The mothers' cars were all lined up in front of the school, while they waited for the children to be dismissed.
Here we have more than one mother with cars, so we follow the rule of adding the apostrophe after the "s."
Here is your sentence with the correct apostrophes for possession:
- The women's locker room looks just like the men's.