Another special pleasure of Heidelberg is taking a boat ride along the Neckar, a major tributary of the Danube. Those who don't wish to spend an entire day on the river may opt for a shorter trip to Neckarsteinach and return which takes about 90 minutes. On both banks of the wide, sparkling river are tree-covered hills dotted with beautiful homes, palaces and castles.

The largest Rhine boats, some of which carry overnight passengers, are 360 feet long, 36 feet wide and weigh 3000 tons. The river for most of its length is about 12 feet deep. During its 127 miles it drops 480 feet by means of 27 locks and joins the Danube at Mannheim.

Our 600-passenger boat had only a captain and one crew member. As we pulled away from the dock I sat on deck alongside other tourists and was lulled by the gentle motion and refreshingly cool, breezy weather. Life took on a slower pace as we passed the red-roofed cities and towns along the riverbanks. The architecture, of course, is from an earlier age and the scene is marred only by the presence of yellow construction cranes thrusting skyward and a modern highway along the riverbank.

About every half-hour we entered locks, watery elevators which raised the boat twelve feet or more. The bow thruster turned momentarily to straighten us out as we moved into a space barely larger than our craft, wooden bumpers shielded the boat's sides, the gates closed behind us and then we waited while the flood of water lifted us to the next level. The trip is a pleasant respite from other sightseeing activities.

River trips: Heidelberg-Neckarsteinach and return 15.50 DM ($11). Lunch and dinner cruises with music are available roundtrip Heidelberg-Rudesheim for 52 DM ($40). Rhein-Neckar Fahrgastschiffahrt, phone 06221/20211.