Northeast Regional to Philadelphia: 1h 30m, $29 if you book 2+ weeks ahead. Leave 8am, back by 9pm for a full day trip.

Philadelphia has incredible food scene, historical sites, completely different vibe from NYC. Liberty Bell and Independence Hall are free. Reading Terminal Market is amazing for food exploration.

Book directly through Amtrak. $29 tickets sell out quickly but $49 tickets usually available last minute. Still cheaper than a Broadway show.