Inner is a synonym of Intimate. Intimate is similar to Personal. Personal is related to Case. 
you are likely to find Towel in/at/on Roof. you are likely to find Towel in/at/on Gym. 
Inner <--Synonym--> Intimate <--SimilarTo--> Personal <--RelatedTo--> Case 
Roof <--AtLocation-- Towel --AtLocation--> Gym 