Musser Park is the green centre of downtown Lancaster, four blocks northeast of Penn Square. The park sits on a single city block, with shade trees, benches, a playground, and a small bandshell that hosts the city's summer concert series. The Lancaster Recreation Commission runs free outdoor yoga and movie nights here in good weather.
It's the easiest place to take a short break between the museums and the market — pick up a sandwich at one of the nearby cafes and eat it on a bench under a sycamore.