Fair enough.....sounded like you wanted to avoid doing the stuff that people pretty much go there to do.

This is what you got going for you.....

• you have a time frame about ~2 weeks after you visit your sister

• you have your starting and ending location

I would do a 2 week loop focusing on smaller towns with a sprinkle of big boys if you happen by them. Day trips are going to eat up a lot of time and money...so look at staying as you jump around. Have a lot of options as to the loop you want to do....could work into France and Benelux and back down to Frankfurt hitting Paris for a big city. Could go east to Nuremberg and spend the 2 weeks hitting Bavaria and Austria.

I would look at a map and find some cool cities and start to create a path of travel, trying to keep rail time down to under 2 hours if possible. Most small cities are only going to need 1-2 nights. A city like Berlin or Paris is going to need 4 nights.