Keyhole gardens are where you build a compost pile in the middle of a raised bed or hugelbed to keep it warm in the winter and to provide nutrients and worms, etc. Pretty cool idea.
There are some pretty neat ideas on that website. Not just keyhole gardens.
It's never too late to start! I retired to homestead on the slopes of Mauna Loa, an active volcano. I relate snippets of my endeavor on my blog : www.kaufarmer.blogspot.com
Dinner will be steamed monkey heads with a side of tiny ads.