The "Berg der Schätze" (Treasure Mountain) in Altaussee is the largest, active salt mine in Austria. The underground salt lake with its multi media tour is well worth seeing. Have fun on the two miners slides.
Good luck in the Salzwelten Hallstatt. The panorama funicular railway you brings you to the high mountain valley of the salt mines. See the oldest wooden steps in Europe in the new Bronzezeitkino 400m underground.