I found myslef with a job for the summer. My company relocated across the country. My sister inlaw who i will call Sil, was planing a vacation to florida to see the grand parents. She asked i wantes to come. I thought it was odd, but it was actually the wifes idea. So i packed and hit the road. After 2 days in the car we got to the gparents house. It is known that when alone they have a tendancy to be nude. Over the years family have given them signs and what novelties to decorate the pool that acknowledges the swimsuit optional way they live. We sat outaise the first night and joked about the signs. We set up a blowup mattress in the spare room. I had the blow up and Sil had the regular. It was like 2 am and we were awoken by the sound of a hiss. The seal broke and the mattress was leaking. I heaed Sil say "just get in this bed." I did and did everything everything i could to stay on my side of the bed. In the morning we sat outside and had breakfast. Boy was it hot. After we ate the gparents said they were gonna get in the pool. Sil agress. She gets up and starts to walk toward the pool. Off comes her shirt and shorts, now totally naked she jumps in the water. She comes up and says she was following the sign, which read "no suits beyond this point", she was laughing. The gparents laughed, shrugged it off, and got in the pool. The last thing i wanted to see was nude old people but Sil was nude. I had never seen her nude. She called over to me and asked if i was going swimming. I almost said no. What if my wife her sister found out. But i couldnt resist. I disrobbed and joined them. Lunch, dinner, swimming, cards and other games, we stayed naked the whole time. When it was time for bed we completely forgot about the mattress issue. Sil said just sleep with me. I dont mind. That night i slept naked next to my naked sister inlaw and tried to keep my hands to myself. The next day exactly the same. No clothes all day. It was very relaxing. We joke and play games. Laughed and had a lot of fun. Me and Sil got close. We talked Bout so much. The weirdness ackwardness was gone. We would hug or touch an arm luke normal. The nudity was almost forgotten about. That night when we wnet to bed Sil started to play with her boobs. She looked and me and said "i jave nothing to hide. You have seen all of me." With that she lowers her hand and begins to finger herslef. I couldnt help but stare. My dick was rock hard. I had to relive myself. I start to jerk off and explode quickly just as i see Sil tense up and shake. She looked over and in an embarrassed voice says "i cant believe we just masturbated infront of each other." We climb under the sheets and start to snuggle. She asked if it was ok and i said yes. Day 3 was raining. We stayed inside....still naked. That night we climb into the sheets and snuggle. I can feel the warmth coming off her pussy. Im abcent mindedly running my fingers on her leg. Her hand slips around my dick and starts pumping up and down. As she is going up and down my fingers work there way to her pussy. I enter and start to finger her. And few minutes pass and we both errupt in orgasm. Quickly we both pass out. Day 4, is back to sunny and hot. The grandparents go food shopping. We stay behind and are horsing around in the pool. Sil jumos in and i grab her to throw hwr towaeds the deeper water. As i do it out genitals rub agianst each other. We pause and she lowers her self. I slide right in. Pumping up and down. Im kissing and bitting at her nipples. She begins to shake and screams. She jumps off and i erupt into the pool. She looms at me and starts to frantically apologize. Im sorry im sorry. Its all ky fault. Please dont tell my sister. I told her not to worry. Its as much my fault as it is yours. I couldnt possibly beging to explain to her that i spent 4 days completely naked with you and the gparents. That i watched you finger yourself, fingered you, then fucked you in the pool. She said thank you and kissed me on the check. The next day we left to come home. When we got to the hotel, the first thing we did was strip naked. That night we fucked again. Since that night we havent fucked anymore. We are incredibly close and hang out all the time now. We constantly flash each other.