Mystic T.
Google
Great art collection especially German expressionists! Jawlensky especially and Kirchner, Nolde, Werefkind, loads more.
Nicely presented over 3 floors and informatively explained.
There's loads more like the brilliantly blackly comic installation The Red Wagon mocks the illusory promises of Soviet communism in the form of a kind of parked-up fairground caravan/attraction.
And the art nouveau/jugendstil offering is spectacular from glass to furniture to clocks to artworks including the famous Ophelia.
You'll spend at least two hours and that's without the natural history sections.
Museum has decent shop plus café. About 10 mins walk from Wiesbaden main station.