I often used my local swimming pool after work during the summer. It was usually near empty by about 8pm and very few people about. One evening after a relaxing swim I retreated to the changing room to dry and redress. The changing area was one big section with multiple lockable booths. I retrieved my clothing and entered a family booth (bigger than the rest). Upon sitting down I noticed someone had left a towel at one end of the bench. I picked it and a pair of red polka dot panties were rolled up inside. I checked them out and the size indicated they belonged to a teenage girl.
I opened them up and found a thin crust along the crotch area. I sniffed the panties and noticed a faint aroma of pussy. My cock was hardening now and I slowly began stroking. I sat on my towel on the bench and held the panties to my nose. I pictured the girl wearing just the panties standing in the changing booth watching me wank. My strokes became faster as I imagined her bending over in front of me, her ass towards my face. I could feel that tingling in my balls so I wrapped them around my cock as I pumped my jism into them. I rolled them back up into the towel, finished changing and left them there.