My wife and I have been naturists for years and take a couple of vacations at the Costa Natura resort in Spain every year. Due to the way our work commitments are we don't always get there together and there have been times when I've holidayed 'solo', or she has, or one of us has joined the other after a few days.
In May 2016 I was sitting naked on the balcony checking social media and my wife had gone to bed to read. My sister, who had never known I was naturist, popped online and we started chatting (in text).
'Wish I was in the sun right now', she said. 'Work's going badly and I need a break just to get my head together'.
I knew my wife wouldn't be able to make it out for our next trip in August so I asked if she'd like a sunshine break then, all costs covered already and the only thing she'd need to pay for was her air fare. 'Would love to', she typed.
By this time I'd downed a bottle of wine

so I typed back 'You're welcome to...but now's the time to tell you I'm a naturist, in a naturist resort right now, naked on the terrace'.
'You're so funny!'
'And telling you the truth'.
There was a bit of a delay, then she started asking all manner of questions about it. How we got into it and so on. And why had she not known before.
'It never came up in social conversation'. The truth is she's never been very good at keeping things secret, so I never mentioned it to her while our probably disapproving parents were alive.
The long and short of it is she joined me, curiosity aroused about the whole naturist culture, in August 2016, but said she wouldn't be going naked under any circumstances.
'As long as you know I'll have my kit off within about 10 minutes of checking in', I told her in the taxi on the way from the airport.
Hey, I'm a naturist, why would my sister's presence alter things in a naturist resort?
So, sure enough, to her embarrassment I was naked within 10 minutes of setting the suitcase down, and off for a swim after some hours travelling, just to feel alive after the awful experience that flying has become in recent years.
And she was embarrassed as much for her own sense of being uptight about nudity as seeing me naked.
True to her word, she remained dressed for a couple of days and would cover up with a sarong, although she became more relaxed by my and other people's nudity.
On the third morning I'd wandered, nude of course, to the shop where you can buy fresh croissants for breakfast, came back, made tea (we're Brits! Always tea, never coffee!), called her to say I'd made a brew and sat down at the breakfast table on the balcony. She came out wearing her sarong, as usual, and had my head down in my tablet, catching up on the news. She sat down, but whatever way she did, the sarong 'snagged' on the chair, and when she stood up to lean over for the teapot, the sarong parted company with her!
So there she was, fully naked and absolutely mortified with embarrassment in front of me.
Of course I knew she was naked but having seen hundreds or thousands of naked women in a naturist environment before it didn't shock me, even though she was family.
She made an attempt to release the sarong which was well and truly stuck between the frame of the chair's leg and arm, then gave up and, although still uncomfortable, continued to eat breakfast nude.
In order to normalise the situation for her, I never made any comment about her embarrassment and simply read out bits of news to her. Of course I was looking from behind my dark glasses.
Not in any sexual sense. Shapely, and of a generation where going bare down there wasn't a thing, but I wasn't looking at her in that way. Just slightly amused by her embarrassment and fluster.
With breakfast over, I thought she might make another attempt to un-snag the sarong and was surprised when she didn't bother, but cleared breakfast dishes fully nude.
After that she'd cover up to go to and from the pool or sea, but was quite content to swim naked in both and really enjoyed the freedom of swimming without a costume, or to sit on the balcony with me fully nude.
In fact, she liked the experience so much that she and her husband booked an apartment for the same resort last summer, and she's now talking about her, her husband, my wife and I having a week there in 2018. From what she told me her husband took to naturism like a duck to water, although she still apparently still felt the need to cover with a sarong when walking between the apartment and pool or sea. She didn't feel confident enough to do the walk fully nude.
There wasn't anything remotely 'exciting' about seeing her naked (even though she's an attractive woman in her early 50s). For me, it was just another woman encouraged into the wonderful world of naturism.
[Another thread asks if we've ever seen a platonic friend naked. At the same resort, yes. I'll add a story on that thread in due course]