The Donau starts to get interesting at Tuettlingen as it begins to carve its way through the Karst limetsones of the Swabian Alps. I spent a few rest days Around Findingen (celebrating its 1150th anniversary). As some will know, my rest days can involve some refreshing 30km hikes, and I walked through some really beautiful forests, up to lookout stones over huge vertical cliffs, to catsles, abbeys and hiostoric towns. The higly ornate abbeys each have their own specialty, and you won't find better wheat beers and fresh smoked sausage anywhere else in the world. I didn't try the flowers.
It's Karst country with impressive cliffs and deep caves. The steadily increasing size of the Donau suddenly disappears into the porous "Versickerung" (= draining away). It's probably no coincidence that this word is pronounced exactly the smae as the english pronounciation of "Versicherung" (= insurance), that great hole where money drains away.