I was nude on a naturist beach on the east coast of Australia. There were a few nudists near me but I became aroused when I saw a lovely nude girl close to where I was sitting. Like most nude ladies on the beach her pussy was shaved. I didn't mean to get a slight hard-on while still on the beach but it happened to me regardless, man she was beautiful.
I needed to masturbate to reduce this powerful urge that had suddenly overwhelmed me. I did not want to do it on the open beach where I would be seen, so I went into the nearby dunes where I was fully hidden. I began to masturbate and had a strong erection. I was looking down at my hand stroking myself and getting ready to watch my cum shoot out when suddenly a lady's voice said, "He's masturbating Stan!"
What a shock! I was startled as I had been looking down and I hadn't seen anyone coming round a corner in the dunes. I thought I would hear someone before they could surprise me, but alas I was surprised.
When I looked up I saw a nude lady and a man. Flustered, I could only apologize and said that I would leave. The man, who introduced himself as Stan, said "Don't leave. My wife, Jenna, and I would like you to continue what you were doing. We'd like to see you finish yourself off."
I was really surprised at what he said and I asked "Do you both really mean that?"
"Yes, of course. We want to watch you do it."
Jenna then said something to the effect that she'd never seen anyone other than Stan masturbating and she wanted to see me doing it, providing that I agreed. So both of them, total strangers, wanted me to continue until I ejaculated. Having got close to cumming before they arrived I decided to do what they (and I) wanted. My erection was slightly reduced because of the shock I'd had but I soon got it fully up again as I stroked it. Another surprise.
Stan put his fingers into his wife's cunt and she held his cock. As I masturbated they did the same to each other. Here we were, total strangers, masturbating and watching each other. I was the first to cum, soon followed by Stan. Jenna was panting as her husband gave her several orgasms.
When we were all finished Jenna said "I totally enjoyed what we have all done. That was the first time Stan and I have done it in front of anyone and I found it very exciting."
I told them that I'd never before masturbated in front of others and had found it exciting too. Now that I knew that the couple were, I told them I was Don. Stan joked "How do you do, Don. Nice to know you" and went on to say that as we had all enjoyed what we had just done together we ought to do it again another time, but not in the dunes. We were lucky not to have been seen.