We hiked the newly opened crosstown trail in SF (https://crosstowntrail.org/) this weekend. It’s 16.5 miles and about 2600 feet of climbing from Candlestick Point to Lands End, though you could easily skip the first section (5.5 miles, 700 feet) if you want a shorter day. Really stunning views of the bay, ocean and (at the end) the Golden Gate and very accessible by public transit.