Especially Autobahn in Germany is interesting. Generally there is no speed limit, but something called "Richtgeschwindigkeit" (the advised speed you should go, which is 130km/h). But there ARE speed limits on most parts of the Autobahn (construction sites are generally limited to 60 or 80km/h, dangerous sections, etc. so it's often limited to 100-140 km/h). Sections without speed limit are a lot of fun and created a whole industry around them. There are car rentals with sports cars you can get for a few hundred/thousand Euro a day, depending on the car (and they have almost everything, from Porsche and Mercedes AMG to Ferraris and Lamborghinis).