I support this recommendation. 
Scuba gives you a very good excuse to take a week (or two) and go to tropical islands (or the ocean coast, if that’s your preference), and see beautiful fish and corals, sunken ships, and funny creatures.
Geocaching is super fun. Nthing that!
Letterboxing is a close relative: Letterbox (disambiguation) - Wikipedia
I really enjoy going out with the metal detector and digging stuff up:
http://flickr.com/photos/kimhotep/179418898/in/set-72157594176847625/
You could learn to ride horses. I don’t know if the dog-oriented stuff that delphica suggested piqued your interest, but there are a LOT of dog activities out there, from straight obedience to training for search and rescue, water rescue, or pure fun competition like flyball and agility. Continuing on the animal theme, there are also plenty of orgs that would welcome volunteers - wildlife rehab or animal sanctuaries, dog breed rescue groups. Animals need a lot of day to day care, scrubbing and poop is often involved. But there are definitely payoffs. A friend of mine volunteered for a long time with a local aquarium, and they went out to collect sick or injured seals, cared for them, and released them. It was definitely a physical job, but she got to be close to some pretty amazing animals, and got to enjoy a lot of cool behind the scenes aquarium stuff.
toadbriar, I looked at the items you found with the detector. I could really get into that! I think the items to the left of the shoe lasts might be a purse frame.
I really like your lists of suggestions. The letterboxing sounds fascinating. I went to your website and found all of the incredible fairy speciimens! I’ve caught a few myself, but they always get away.
Kite flying?
There’s all sorts of designs and sizes, and if you want to take it further there’s also kite-buggying, kite-sailing, kite-surfing and kite-skiing!
I was just going to suggest that. I’ve just ordered my first power kite to give it a try. From the looks of it it could be very strenuous depending on how big a kite you get.
I’d also suggest wood turning. I took an introductory course a few months ago and am saving for my own lathe and tools. It is relatively easy to do as a beginner to create items from pens to large bowls. Yet it is challenging enough that it takes quite a while to become an expert. Also, you create great gift items for friends and family.
I just stopped by to say I misread the thread title as “Recommend a New Hubby to me!”.
I second the suggestion of sailing. Particularly on lakes you can often find rental or club arrangements that are not expensive. Given your Silicon Valey location I’d suggest that SF bay is NOT the place to look for inexpensive sailing options.