I am staying in St Goar a couple of days and want to tour a castle one of those days. Any recommendations on which castle is the best choice? We will have a car.
An obvious choice is Rheinfels Castle right at St. Goar. If you want to drive, cross the river (ferry) and drive up to Marksburg castle. It’s only about a 30 minutes drive. About an hour’s drive away is Burg Eltz. Those are the only castles I’ve visited in that area.
ETA: when we visited Marksburg castle in 2023 you couldn’t wander on your own at your own pace. Tours were every hour and there was only one English tour in each the morning and afternoon. At the time, the afternoon English tour was at 1pm.
Not sure what "best" means... Marksburg is the closest intact medieval castle to St Goar which you can tour; it invokes the Middle Ages more effectively than any other castle in the area. It is open year-round. Use the St Goar ferry crossing and drive north to Braubach. Or drive via Koblenz.
Burg Eltz is a longer drive and more similar to a residential palace than you'd expect for a medieval castle - Family-occupied for centuries, it's packed with lots of "froufrou" furnishings from more recent periods of history. It is also worthwhile. Note that it closes Nov. 1.
A plus for Marksburg is that, in addition to the onsite food service (nice views of the river valley up there,) the very handsome old town of Braubach, at the foot of Marksburg, makes for a delightful visit and has several places for lunch; it is an easy tangle of old-world streets to cover on foot before or after your tour.
https://farm5.staticflickr.com/4143/4751924826_98980aa49f_o.jpg
https://fotos.schloemp.eu/wp-content/gallery/braubach/002Braubach-Bauernschaenke-Eck-Fritz.JPG
https://delveintoeurope.com/braubach-germany/
Rheinfels is closed for renovation and it's due to open, but it's still covered in scaffolding. Marksburg is probably the best known for it's tours and ability to see something of the insides of a castle. Stolzenfels Castle is also in the middle of renovation work. I'd seriously give thought to Rheinstein Castle; beautiful, great views, less visited, and open.
But if you want to see the most impressive fortifications you need to go to Koblenz and tour Fortress Ehrenbreitstein.
Thanks for all the input.