Photos: Mliu92 · CC BY-SA 4.0 (1, 2) · Dan Dascalescu · CC BY-SA 3.0 · Dennis G. Jarvis · CC BY-SA 2.0 (4, 5)
Free. Walk it downhill from Coit Tower to face the bay, and stop halfway at Napier Lane, a boardwalk of 1850s cottages. Neighbours' front doors are right there, so keep your voice down.