Well the Barrier Reef was a full day's trip but I spent most of the journey there and back indoors / below deck.
I didn't do any swimming / snorkelling / Scuba diving. I did sit on a beach for a bit and watched the birds. Then I went on the, not sure what it is called, a boat but you go downstairs and where you sit is underwater and you can see the fish, reef, coral etc.
In Oxford it was May Day and I had a walk with some friends around Christchurch meadow.
I do spend a lot of time indoors. On Monday my carer and I plan to go to the pub, it has AC and Mondays are quiet.
I will have completely covered me in factor 50, I will have a shawl / throw with me to put over my arms if I wear a T shirt. I will be wearing a hat with a wide brim.
He will wheel me to the bus stop, about 5 mins, the wait for the bus is about 10 mins max, and the bus stops very near the pub. Then we will do the journey in reverse after lunch and some alcohol.
It is quite a few years since I have burned but as you say skin cancer is not worth it.
When my niece and nephew were young ( they are fully grown professional adults now) I had a trip to Oz and one thing I bought for them were bathers with arms and legs. You can buy them here now.
Also some Australian clothes actually have a UV rating on them. I wish that happened here.