day trips from Frankfurt without a car

Bad Homburg is a Frankfurt suburb with S-Bahn trains every 15 minutes and take about 20 minutes. Limburg(Lahn) and Michelstadt have hourly regional trains and take about 1 1/4 hours, These are all local network tickets.

Yes, the train system is extensive with frequent trains, maybe not as punctual as it once was. Some of those places using buses and trams in conjunction with D-Bahn trains, and Regional services might be useful.

Figure out what a decent amount of time to devote to a train trip and go from there. All the towns you mention are within a half hour to less than two by regional train. Others might be the smaller towns along the Rhine (Bacharach, Boppard, St Goar).

There are usually day passes for the region to make travel cheap, which one, and how many regions you might traverse will determine the cost. If your travels are more extensive in Germany, then look into the Deutschland Pass.

Bad Homburg

As @Sam said, you can take the S-Bahn to Bad Homberg. Once there you can walk about 15 minutes to the pedestrian zone or take one of the busses that you can find right outside the train station.

Bamberg is kind of far for a day trip.
Limburg is only an hour away by train as is Marburg, Seligenstadt, Büdingen. Idstein, Mainz, and Wiesbaden are about 45 min. Michelstadt is farther, about 1.5 hours and their Christmas market isn't open every day. Bad Homburg only has its' market open on weekends. (wasn't sure if you were coming for the Xmas markets or not)

I believe the OP said Bad Homburg, not Bamberg.

Thank you everyone! This is so helpful! We will be going in late May, so no Christmas Market expectation. After the few days in or around Frankfurt we are going to Strasbourg by train. Are there places to see in that direction? Looking for historic, picturesque towns reachable by train and walkable when we get there. Trying to decide whether to stay near the train station in Frankfurt or venture to another town to base ourselves for 4 nights. Any suggestions/recommendations are very welcome as we have never been to this region before.

If you are staying in Frankfurt, stay in the center of town, near the Hauptwache and not near the train station. You can be at the station by train in a couple of minutes from anywhere in the city.

Try Motel One Römer, Flemings City Center, Hilton, Moxy, Ruby's, or the Steigenberger Frankfurter Hof. This give you easy access to all the main sites in Frankfurt and all of the dozens of museums. Depends on your interests really. There should be some festivals in May and the Farmers markets downtown are great.

If you make the short trip up to Bad Homburg (very nice) you could also pop off at Altstadt Oberursel and have a wee squint at that nice place. Good atmosphere and food at the Alt-Oberurseler Brauhaus too.

Heidelberg is great also Mainz.

Take a short river cruise from Rudesheim.

You have a good plan, but consider a few complicated details:

Most rail networks, especially Frankfurt's excellent S-Bahn network, are "radial". That can make it very hard to visit two or three towns in one day, unless they are on the "same" rail line. For a big destination, a full day is fine. But (for example) many towns on the Fachwerkstrasse have relatively small historic centers, not a full day of visiting. This also tends to argue against staying in a magnificent (???) small village that Band of Brothers just left (Ironica typeface!), because you have to "go back" to the Frankfurt HBF to go somewhere on a different train line?

Many major Euopean capitals still have the problem of the main train station area being a bit gritty or sketchy. Compared to the US, street crime in Europe is rather low, but unless you can't afford a nice hotel, it's not always a good idea to stay near the main train station. It also betrays a misunderstanding of urban life; mass transit is a daily need, and especially in Europe, well provided for. Sometimes it's faster to walk to the train station, and that walk can include attractive areas.

Have you already seen the scenic Middle Rhine Valley, from a K-D dayboat? The river is not so scenic in Frankfurt, but trains can provide easy access to the scenic Bingen-St. Goar segment of the river.

My trip report involves a car rental, but I am not contradicting the idea of train travel, which is equally practical for what you want to do. But if you can plow through all my writing, you'll read about some of the towns and cities we liked:

https://community.ricksteves.com/travel-forum/trip-reports/baltic-germany-fachwerke-landesgartenschau

Looking for historic, picturesque towns reachable by train and
walkable when we get there. Trying to decide whether to stay near the
train station in Frankfurt or venture to another town to base
ourselves for 4 nights.

Staying in a different town will probably mean a different set of day trip destinations.

Would you be looking for something comparable to Frankfurt? Frankfurt, a large, modern city, has a population of 800,000. Cologne is big too, a little bigger than Frankfurt at 1 million, but it feels a bit smaller and a little less modern.

Heidelberg (160,000) and Mainz (220,000) have been mentioned as well... could be good choices. Either would put you within striking distance of Strasbourg (nearly 500,000.)

When I explore some part of Germany that is new to me, I usually pick a much smaller, more atmospheric base town to stay in, preferrably a place that is 100 times smaller than Frankfurt, but one that still has good rail connections to other places. You would be surprised at how many small towns in Germany make for perfectly functional travel bases for train travelers.

One place that Rick Steves' guidebook recommends - Bacharach, population 1,800 - is popular with many people on this forum and a good example of such a place. Bacharach is packed with half-timbered buildings that are much like the ones in the "Little Venice" part of town in Strasbourg. Bacharach is in the Rhine River Valley, not far FRA airport, Frankurt and Mainz. One of my favorite forum members returns there quite often for repeated stays of 3-5 nights. Outings you can do from Bacharach include old-world towns nearby (Oberwesel, Rüdesheim, Boppard, Braubach) as well as castles from medieval times (Rheinfels in St Goar, Marksburg in Braubach, and Burg Eltz on the Mosel River.) River cruises of 2 hours or so through the Rhine Valley, a UNESCO World Heritage site, are popular too.

https://www.expedia.com/Bacharach.dx6048652

Bacharach, like other towns on the Rhine, sends off frequent northbound and southbound trains trains to get you where you are going. On the opposite river bank, Rüdesheim and Braubach are connected by the railway as well. All the riverfront towns between Bingen and Koblenz on both sides of the river are compact and easy to explore on foot. If you like scenic views, you will find chairlifts and cable cars in Boppard, Rüdesheim and Assmannshausen which take you to the river gorge clifftops for fine views - and refreshments too. This place is near the top of Boppard's chairlift:

https://s3-media1.fl.yelpcdn.com/bphoto/T9oxNMwLvt_-r5nCsce-jg/o.jpg

Well, on your way from Frankfurt to Limburg, you could stop off in Eppstein that has a cool castle ruin as well as Idstein, known for outstanding, carved Fachwerk buildings, just like LImburg is. The Union church in Idstein is unique and stunning. The cathedral in Limburg is ancient and beautiful.
On your way from Frankfurt to Büdingen, you could stop off in Gelnhausen, both are chock-full of fachwerk buildings and ancient churches. Gelnhausen has a fabulous ruin of Barbarossas palace. It was much larger than what I had expected and well worth a visit.

Don't write off Frankfurt as some people on this forum do, it is full of historic sites and is one of the oldest and most important cities in German history.

Looking for historic, picturesque towns reachable by train and walkable when we get there.

As a day trip from Frankfurt, consider Miltenberg. Do a google search and see what you think.

By train Fulda ca.1hr by regional train or ICE

https://www.region-fulda.de/tourismus/

Christmas Market in Fulda https://www.weihnachten-fulda.de/

uwe, you need to read all of the posts. They are going in May.

No reason not to go to Fulda for a daytrip ;o)
Thank you