Echo Park Lake in Los Angeles has a loop that is about 1 mile around. It’s a pretty busy park, that has ducks and geese everywhere. Beautiful lotus blossoms and iris flowers in the lake. Generally flat and one tiny incline that can easily be avoided. You can also rent swan paddleboats that light up at night. There is the chain link fence that now encloses the park, surrounding the lake, which sadly was put up to keep the homeless out. It makes it harder to access the park, with only a few points of entry that you have to look for.