Boating in Golden Gate Park
This large park in San Francisco forms a significant part of the city (very evident on any map). It has a variety of attractions and many places to just chill out.
Although the park gets an estimated 13 million visitors every year (!) it's so big - 1017 acres it doesn't seem crowded.
There are many different areas & attractions, including - seen here - Stow Lake, which dates from 1893.