Half day in Munich

With only a half day, I'd return the car unless you are returning at airport. I would enjoy the old part of the city...clock and church

Wander thru the old town, check out the market, have dinner at a Biergarten. The Hofbrauhaus is lively in the evenings.

It's unfortunate that you don't have more time as there's so much to see in Munich. The Deutsches Museum is one of my favourites! I agree with previous replies that spending some time in Marienplatz would be good for a few hours. If you're interested you could have a look at the Hofbräuhaus and perhaps have a beer (or two).

I usually make a stop at this restaurant for dinner, which as I recall is close to the Hofbräuhaus - https://www.opatija-restaurant.com/ (sorry I don't know how to translate the website).

Here is a suggestion from a previous thread, keep in minds this is a morning iteneary assuming the person starts at the Airport so adjust as needed:

Here is what I would do:

• 06:30 - First, purchase an Airport-City- Day-Ticket from one of the MVV ticket machines (super easy, just change the language to English using the flags at the bottom of the screen). This gives you unlimited travel on all public transport for the whole day.
• 06:44 - Take the S8 from MUC to Ostbahnhof (if you miss the 06:44 the trains run every 20 mins)
• 07:15 to 08:00 - Arrive at Munich Ostbahnhof, if you picked up luggage you can leave it here. Most of the good restaurants don't open until 8 so take a little walk around Haidhausen, settlement since 808AD, and see how people live their lives. Go strait out from Ostbahnhof put you in Orleansplatz, check out the fruit and flower sellers setting up their stalls. Continue up Wörthstrasse through Bordeauxplatz and admire the gardens in this long leafy square. At the end of the Platz take a right on Metzstrasse then a left on Preysingstrasse to see some historic houses including a relocated alpine hut that is now the HQ of the Munich Alpine Youth Club. Keep walking down Preysingstrasse and right before Fruchthalle on the right head down the alley to for a quick peak at Johannisplatz (the square around the church). Head back through the alley, continue on Preysingstrasse and make a left back onto Wörthstrasse headed to Cafe Voila for breakfast at 8am.
• 08:00 to 09:00 - Cafe Voila is about a half block back down Wörthstrasse, I recommend the traditional Weisswurst, Breze (Pretzel) and Weissbier.
• 09:00 til noon - exit the Cafe and just to the right is the stop for the number 19 tram. Take the next one and enjoy the sights through Haidhausen, around the Maximilianeum, and down Maximilianstrasse and get off at Nationaltheater. Now you are in the city center. You should have enough time to hit most of the sites on the Rick Steve Audio Walking Tour.
• Noon til 1pm - Head to the Viktualienmarkt for a Biergarten and lunch experience. Once you are done head back to the Marienplatz to catch the S8 or S1 to catch the S-Bahn back to the Airport before 1pm (up to 1 hour transit back to airport). If you take the S1 remember to get on the right car as it separates at Neufahrn and part of the train goes to Freising and part goes to the Airport. You'll have many chances to switch if you get on the wrong car, just ask the other people on your train "Airport?" even if they don't speak English they will help you (Germans are happy to help strangers).

Have fun!

DJ

You don't list a starting point or interests but I found the best day included a little of everything. Start with a walking tour downtown and don't miss the Marienplatz, Viktualienmarkt, and a few of the churches. Find a walk that suits your tastes. Then make your way to the front of the Hauptbahnhof and get on Tram #17 towards Nymphenburg. Tour Nymphenburg then walk to the Hirschgarten (beer garden). Enjoy a beer and some food. Get back on the tram and return to town. If you want stop at Augustiner Keller on the return for another great beer garden.