This is one of the three for-fee parking garages/lots around Altstadt in Regensburg. It's…read moreconveniently located not too far from the center of activities...it's at the western edge of the Old Town just around the corner from Schottenkirche (Scottish Church or Scots Monastery). As the name suggests, it's near the theater.
If you're not paying attention too closely, it's very easy to miss when you're coming from the north on Bismarkplatz. If you are approaching from the south, it might be more noticeable and you can make an easy left turn in to the underground ramp (photo).
We parked there for a little over two and 1/2 hours, and the fee was 4.50 euros, so it wasn't too expensive. It's cash-only...there were two other machines, so you may have been able to pay it with a card with them...(I just went to the first available one and didn't check others out).
