Maybe not a must see, but a nice trip destination just outside of Munich. Easy to reach by public transport - since December round trips Tutzing (Lake Starnberger See) - Andechs - Herrsching (Lake Ammersee) are even easier. And while the "Holy Mountain" is only a small hill one has nice views e.g. on lake Ammersee. With the right (rather rare) weather conditions even such views are possible
(Andechs monastery in front of - the nearly 90 km away - Zugspitze)
The church is also quite interesting. In a side chapel there is the grave of the composer Carl Orff ("Carmina Burana" - the most performed choir piece in the 20th century).