Staying over in Rhine Rive Valley or late night train to Munich

You will have to decide: either on an evening train to Munich (last departure 19:36, arr. 00:27) or on the sunset on the Rhine. Well, a third possibility would be sitting (!) all night in a train that is meandering through SW Germany and stopping every 10 to 15 minutes. (Bacharach dep. 21:36, Munich arr. 6:02).

Bacharach is where there is a castle hostel. Reservations need to be made well in advance. I have never really noticed the sunset in Bacharach

Thank you all for your value inputs. Checking on the train schedule from Bacharach to Munich, I realized it requires some train changes, and some are quick ones. I am going to travel with a 12 year old. It would be kind of difficult to rush like that at night. It would be reasonable to just stay over night in Rhine River Valley area, and go to Munich the next day during the day.

Braubach has a very attractive Marktplatz where you can have a nice meal.

After that... St. Goar? Rheinfels is the only real sight in that town. Were you hoping to tour another castle as well? You might instead stay on that train from Braubach and get off to the south in Ruedesheim, where there's more to see and do. Check out the Castle Cruises and the Ring Ticket options on this page. R'heim has a chairlift ride you can take and several other sights/activities in town. Stay in R'heim if you wish.

FYI Bacharach's castle hostel is a seriously-steep climb from the center of town.

Early train from Cologne to Braubach, then visit the Marksburg Castle.

The Marksburg can only be visited with a guided tour. Unless you are planning to take a German language tour, you won't need to take an early train. The first English tour is at 1:00 PM. Even by regional train, the trip from Cologne to Braubach only takes an hour and a half. You could leave Cologne on the 10:32 RE and change in Koblenz (12 min) to the next VIA train up the right bank, and get to Braubach at 12:05. That's enough time to climb the hill and get on the 1:00 PM English tour.

The tour take 50 minutes, and the next train to St. Goarshausen leaves Braubach at 2:06 PM. I don't think you can get down the hill and to the station in 16 minutes, so you will probably take the 3:06 PM train and get to St. Goarshausen KD dock, next to the ferry by 3:40 PM. If the ferry is running on schedule, you just make the 3:40 ferry and get to St. Goar at 3:45. The last KD boat to Bacharach leaves St. Goar at 5:10 PM, giving you 1H25 to see St. Goar. Considering the time to get up to Rheinfels castle and back down and buy tickets at the KD kiosk, I don't think you would have much time at all to see the castle, which, IMO, is just about the only thing in St. Goar worth seeing. Plus, the 5:10 PM KD boat to Bacharach get you there at 6:30 PM. The next train after that leaving Bacharach is at around 7:00 PM, which doesn't give you time to see Bacharach. After that, there is only a night train connection leaving at 9:00 PM.

Bottom line, you either need to leave Cologne earlier and take a non-English language tour of the Marksburg, or you need to spend a night on the Rhein, preferably in St. Goar (or maybe Braubach, Boppard, or St. Goarshausen).

Plus, we haven't addressed what you plan on doing with you luggage all this time.

The TI office in Braubach is near the station and will hold your bags (as long as it's open.) You can request an printed English-language guide and follow along on the German tour.

I really appreciate all your value inputs. Lee, you have a very good point about the luggage. What if I changed the plan a little bit. At the end of the day, I will stay over at Bacharach. So, in the morning, I will take the train from Cologne to Bacharach, drop the luggage at hotel, take the cruise from Bacharach to St. Goar, then ferry and train to Braubach for the English tour. After all that, I will take the train back to Bacharach. I am going to use the German rail pass, the cost of extra train trip does not matter to me.

I would stay over night in the Rhine Region,head to Munich in the morning.I would take the high speed train out of Mainz,it has no connections and is about 4 hours.I think it leaves around 10:15am.Gives you time to take the regional train down the Rhine to Mainz.Check out the timetables on Bahn.de.

If you only cruise on the Rhine from St. Goar to Bacharach, you are missing so many castles and gorgeous scenery. Do consider starting a bit farther away, like in Bingen or Rüdesheim. That short little cruise makes little sense to me. Not sure why RS recommends this Bacharach-St. Goar cruise.
Train to these towns and cruise the other direction so that you are going with the flow of the river.

What else can you see in St. Goar? The ancient church here is certainly worth a visit. Burg Rhinefels is my favorite castle and I recommend visiting this over the Marksburg. Personal opinion of course, but for me it is far more interesting.
A visit to Ober-Wesel is nice too, with another ancient church. There is little to see in Braubach other than the Marksburg and lots of half-timbered buildings, though every town along the Rhine has plenty of those.

Another reason to avoid the late-night trip to Munich is that relatively few hotels in Europe have 24 hour receptions. If you are arriving at a hotel for the first time late in the evening, you should always warn them in advance and recognise that they are going beyond the normal to help you.

Thank you all again for your value inputs. I did some research and agree with visiting castle in St. Goar instead of Marksburg. To me, it is more real and ancient. I think the ruin portion of the castle makes more interesting to me. Yes, will consider taking the cruise starting from Bingen to St. Goar, and visit the castle there. Definitely take the train next day to Munich. Thank you all again.