I just day tripped to Puchburg am Schneeberg and took the Schneebergbahn up the mountain basically for the views, some minor walking trails and a meal. When I got to Puchburg around 11:30am today, all the steam train tickets were booked, so definitely book those ahead of time if you're interested. They only run on certain days and specific hours.

I think you really only need a few hours up there unless you are really going to be walking those trails. But it is a nice place to go if you want to beat the Viennese summer heat and enjoy some views.

If you're going to a lot of destinations in Vienna and Lower Austria, consider getting a Niederosterreich Card. It's about 83eur. The Schneegburg Rail up and back down is about 44eur, so it's worth considering depending on where you go. I was a dumb dumb and went to Melk Abby the day before and didn't realize that was covered by the card (didn't buy one until today). 16eur I'll never see again. Not convinced price was worth it tbqh.

I'm doing a lot of travel because I'm also trying to make back my Vorteilscard (71eur). I've saved about 40eur so far with the discount (50% off regular OBB tickets) for the Puchburg and Melk trips but man, didn't realize how much rail travel I would have to do to break even.