Prior to 21 Days in Europe tour

Yes you can, on www.bahn.de you can add intermediate stops and for how long you want to stop there.

"We are flying to Frankfurt a few days before our tour begins in Amsterdam. We are taking the train from Frankfurt to Heidelberg to spend 3 days..."

I was just reading on another forum some comments made today on Heidelberg from a well-traveled forum member who routinely gives solid advice. He wrote, " I do NOT understand Americans' interest in Heidelberg except that lots of US soldiers were stationed there." My experiences there have left a similar impression - a nice enough place as places go, but nothing particularly exceptional.

I mention this not to upset you but just to suggest that you might want to make an independent stop in either the Upper Middle Rhine Valley - A UNESCO World Heritage site or the Mosel River Valley. I realize that your tour offers a visit to Bacharach and St. Goar's Rheinfels Castle. And these are nice places to visit, but all told, the tour time you have there is too short.

• Rheinfels (ruins) is worthwhile, but you will miss out on a tour of the real castle gem on the Rhine, the Marksburg, a fully-intact medieval structure in the old-world town of Braubach.

• Rick's cruise (listed as a 1-hr. cruise) is likely the 40-minute cruise between Bacharach and St. Goar - a pretty stretch of river no doubt. But this cruise covers only a few km of river and will SKIP the other half of the Rhine's most scenic river segment (the part between BINGEN and St. Goar) in order to save time; doing the whole cruise from Bingen requires 1.5 hours and is worth every minute.)

• Also - there are wine rooms and gardens (like this one in Boppard) and exciting chair lift rides (like this one in Boppard) as well as vineyard walks to lookouts (like this one in Oberwesel) and recommended trails that circumnavigate old town walls (like this one in Oberwesel.)

• The Mosel River Valley has an equal number of charming old-world towns - including Cochem... Bernkastel... and Trier (the better known destinations.)

Anyway - before you lock in Heidelberg, a city of 160,000 with a certain "meh" factor to it - and a big detour from your FRA - Amsterdam trajectory - I encourage you to examine these options, which will also save you some overall travel time.

Thanks for your suggestions, we are visiting Heidelberg because my husband went to school there some 40 years ago.

Oh my... 40 years. He must be very eager to see the place. After 4 decades, my 70's German campus was only marginally recognizable. My Mainz dorm and the on-campus pub across the grassy forum were... gone... with a shiny new glass/steel structure in their place.

Well, on your way to A'dam after his pilgrimage, you might consider a stopover in that area north of Mainz and south of Koblenz which I spoke of. A visit to Marksburg would be feasible with a scheduled stopover at Koblenz Hbf of 4-5 hours; after stowing bags in a locker there, it's only a 10-minute train ride to Braubach. Then a walk to the castle.