Downtown Lancaster is small and flat enough to walk in 20 minutes from end to end. Most of what you came to see — the Central Market, Fulton Opera House, the small museums, the restaurants — is within a few blocks of Penn Square.
Red Rose Transit Authority runs local buses to the surrounding towns and Amish areas, but service is infrequent. To reach Wheatland, the Hands-on House children's museum, or the surrounding Amish farmland, you really need a car or a taxi. Lyft and Uber both operate in the city.
For the farm country east of town — Bird-in-Hand, Intercourse, Strasburg — driving is essential. A common day-trip approach is to base in the city, drive out for half a day to the farms and covered bridges, and walk the downtown in the evening.