You might not have the energy you once did, but you need to be wiser about how you expend it. Time spent not doing what we love is time wasted. If you are still fit and enjoy the company of others, have you ever thought of becoming a tour guide
Become a tour guide when you retire

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Some retirees welcome in cruise ships.
Many find their experience of a museum or art gallery heightened when they are taken around by a tour guide. Museums are always looking for tour guides and sometimes this means only having to be a guide for a few hours a month which may work well for your lifestyle.
Short and long nature hikes are popular amongst tourists and if you are fit and maybe a member of a tramping club, you could think about taking guided nature hikes.
The other day I spoke to a retiree who was a tour guide up from the South Island being a guide for a month-long tour of New Zealand. He just does it on a casual basis with most of his winter spent by his cosy fire. He loves the chance to get out and see New Zealand and the busloads of tourists are always different and interesting.
Being a tour guide offers flexibility, an opportunity to earn, and being able to engage with people as enthusiastic as you about a subject. It is a perfect choice for retirees.