How do I find rooms or reasonable hotels on short notice in Germany?

My teen daughter and I will be renting a car and visiting several smaller cities in Germany in a couple of weeks - Heidelberg, Wurzberg, and maybe some other smaller cities (we're on a castle hunt!) I'd like to drive and maybe find a small hotel or room as we go, but I'm not sure if this is possible or recommended.

Zum beispiel - In the US, I can easily drive until I get tired, find a cheap motel in almost any town, and have a clean place to sleep. However, I'm not fluent in German, though I do speak some, and am not sure how to go about setting up a room on short notice in Germany.

Are there a tourist centers in towns that can set up rooms for travellers on short notice? How do I contact them? I'm interested in just the basics - nothing fancy. A bed and a shower in a clean room will be great. Families who rent rooms would be great if we can figure out how to contact them. I like the freedom of not to being tied to a specific itinerary. Advice is appreciated!

Thank you! Vielen Dank!
There are tourist centers in the small towns, you find them in the phone directory (www.telefonbuch.de), or "en lieu". They're easily to be recognized by a big "i" sign, that means "(tourist) information"; the German word would be "(Fremden)Verkehrsamt", but is rarely used nowadays. Also, when you drive through villages, there are a lot of private B&Bs waiting for guests; just stop by, walk in, and ask for a room. The sign usually reads "Zimmer frei" ("rooms to let"). In my area, which is southeast Bavaria, an average price would be around 35 to 40 Euros per person and night, breakfast included. These rooms are usually rented by families, and some I know even allow you to use their private pool in the basement and their sauna, all in the price. So wherever you see a "Zimmer frei" sign, stop and ask; it's a B&B. Some will be really cheap and friendly, some will try to overcharge you, but in that way, I think Germany is no worse than other countries. They usually have checkout time at twelve noon, so it's best you stop by in the afternoon, but before it gets dark, that's around 3-4 p.m., or 15-16 hours, as we Germans would put it. Chances are best then.

And if you don't find a room at once, don't despair. People mostly are so friendly they tell you where you can stay the night near the village. Germany is densely populated, so there's no need to drive for miles and miles; mostly you'll find proper accomodation "just around the corner".

Enjoy your stay, and happy "castle hunting"! You chose the right area.