Melk Abbey — the Baroque crown of the Danube
Climb to a vast ochre-and-gold Benedictine monastery riding a bluff above the river, where a frescoed Imperial Staircase leads to a Marble Hall and a 200,000-volume medieval library that inspired Umberto Eco's 'The Name of the Rose,' all capped by a riotously gilded Baroque church. It's the single most famous interior on the Austrian Danube and the one a first-timer would most regret skipping. From Krems it's ~40 min by road or the classic upriver boat approach — budget a half-day and use an operator that guarantees you back to the ship.