Idstein is a small town to the northwest of Frankfurt. Its about 30 minutes away by car or train. Anyway, they close off the centre of town to hold a jazz festival each year, setting up ten stages (plus some evening concerts in bars/restaurants). Ok, it isn't Montreux, but it is well recommended and attended. As with Montreux, there are all kinds of music, not just pure Jazz, but that is the speciality. Prices are 15 Eur for the weekend or 10 Eur for Fri and Sat (each) and 5 Eur for Sunday. On both Friday and Saturday nights, the bahn are running a special late service (00:24) back to Frankfurt Hbf (01:02).

As with a lot of such fests, the town centre is filled with food and drink stands so you won't go thirsty or hungry. If you do go by car, please note that you will have to park on the edge of town (see the festival link for info).