Any unknown discoveries you'd recommend

When you are in Reutte go across the border to Fussen. Beats the pants off it. Probably the only thing Reutte has going for it is the Sommerrodelbahn.

I'm afraid I can't totally agree with James' statement that if it isn't in the guidebooks it isn't worth visiting. I have loved traveling off the main roads and coming upon small appealing villages or beautiful scenery that was well worth seeing. I recognize, though, that those of us who live in Europe have the luxury of making frequent day trips or weekend trips that would lend itself to such wandering. People on vacation with limited time may not be able to. I don't have any specific recommendation for the OP, except to say that if you have the time, try to get off the main roads when traveling from one city to the next and just see where it takes you, particularly if you see on your map that there is a national forest nearby.

One of the biggest differences between living here versus visiting is that there's all kinds of stuff that might be worth the quick drive or hike to see if you live near it, but isn't necessarily worthwhile to fly over the ocean just to check out. For example, within an hours drive of where I live, there's probably about four dozen or more castle ruins and watch towers, thousands of old border stones, thousands of kilometers of hiking trails, countless beautiful old churches, acres upon acres of vineyards to walk through, many historical town centers, etc. Of the above, there are only a few that I recommend visitors going out of their way to visit, and of the handfull or so that I usually recommend, only about half aren't in any English language guidebooks (that I've seen). That being said, if you're going from Frankfurt to Rothenburg, I might recommend a detour through the Odenwald. The beautiful town of Lindenfels is worth at least a drive by, and the view from the castle in the center is amazing. Michelstadt is also worth a quick 30 minute visit- sort of like a smaller Rothenburg with only a tiny fraction of the tourists. And it's not really an unknown discovery, but most people I know that have stayed in Reutte (soley because Mr. Steves recommends it) report back that they saw many other towns where they wish they had stayed instead.

I love traveling off the beaten path and enjoy just soaking up the lifestyle of the country I am visiting as much as seeing the 'must sees'. I stayed in a tiny little village just outside of San Gimi called San Donato. There are about 2 small guest houses and a winery there, a little church and not much more, but the view of the vineyard below and the peacefulness was perfect. When I arrived there were a number of artists scattered about painting the scenery. It was a scene from a movie! Someone from the winery also recommended a restaurant that was near the bottom of the hill on the road out of town. It was marked by a tiny hand painted sign hidden by foliage. I followed it up the dirt cow path and at the top of another hill was a spectacular restaurant. It was all locals as far as I could tell, and very fun.
In Germany I spent some time in the village of Bad Groenenbach and it was delightful. I attended a festival there, went to a horse show and stayed at a little guest house in the country. It had a restaurant in it and the white asparagus was amazing. Just a normal little village without any 'tourist attractions.' Loved it.

Yes, I agree that perhaps you wouldn't travel across the ocean solely to see the types of sites I mentioned in my previous post. But if you're driving from one major site to the next and can work it in the way the OP seems to want to do, it's well worth it to get off the major roads.

Getting far from The Madding Crowd in Venice spending a good portion of a day on the East end of the island. Watching mothers and grandmothers with children, couples strolling, families with dogs, picnickers, all enjoying the Park of Remembrance. Great place to watch the sunset.

A discovery I would NOT recommend is that you have a big drop charge on the car. You should definitely know in advance what it is.

If you want places where you won't see the old people carrying their blue and yellow bibles Who you callin' old, James? I hide my RS books in a Kindle. :-) Venice: wander in Cannareggio, through the Ghetto. Not nearly as many people as San Marco. Very enjoyable neighborhood. We also liked the tower (campanile) at San Giorgio Maggiore, a 5 minute vaporetto ride from San Zaccaria, but no crowds and a better view than the campanile in P. San Marco. Also, try to see the city early, as the sun rises and the city "wakes up." Few tourists as the locals go about supplying and cleaning the city. Grab a coffee at a bar and take a dawn walk.

If you are driving from Frankfurt, your GPS will bring you first into the newer (less charming) part of Rothenburg and then into the old walled city. If you have a good map (and won't be too jet-lagged) look for a place to leave the autobahn and come into Rothenburg from the countryside directly into one of the old gates. It can be magical. The GPS does not want to take you this way but you can trick it by putting in the names of one little town after another. (Or you can just follow a map!)

Thanks everyone for your suggestions. The beauty with a GPS is that even after exploring, the GPS will point us back in the right direction. Nigel, we have tickets for the castles before spending one night in Reutte. And the Sommerrodelbahn looks like a blast (after watching a uTube ride). I've not seen this type of "ride" down a mountain before. I've only seen/experienced the Alpine slides in Colorado. Thanks for the suggestion. Tom and Ruth, Thanks for the suggestions on alternatives to Rothenburg from the Autobahn. Claudia, Thanks for the Venice tip. We've been told to get lost, but good to get a recommended direction to get lost in. Laural, I too will have my kindle. And thanks for the Venice tips. Jeff, Since we are flying on miles, the direct United flights from SFO were to Frankfurt. So the $3000+ we saved on airfair more than pays the $500 one way drop charge. We also looked at trains, but Fussen to Lake Como wasn't mean to be traveled by train, and then we needed a car for the week in Tuscany.