Hiya,
check out this link to Eventim, there's a picture. It looks to be an open air on a BIG market square.
http://www.ticketcorner.ch/Tickets.html?affiliate=TCS&doc=artistPages/tickets&action=tickets&fun=artist&key=1750759$8827511&language=en
Herren Acker (an acker usually refers to a field, probably a reference to it's past when it was still a market town and this was where all trading was done).
Have fun,
P.
It looks like it's all standing.