The most enjoyable way to arrive in Neckargemünd is by river boat from Heidelberg. The Rhein-Neckar-Fahrgastschifffahrt runs seasonal cruises along this stretch of the Neckar, and the two-hour journey upstream passes through some of the prettiest scenery in the Odenwald: wooded slopes, ruined castle towers on the ridgelines, and the villages of Ziegelhausen and Kleingemünd along the way.
Boats depart from near the Stadthalle in Heidelberg in the summer season. Check current schedules at the operator's website. Returning by S-Bahn (line S5 from Neckargemünd station, 15 minutes to Heidelberg) makes for a satisfying one-way trip.