Yeah, it's a Tennis Arena - so not a football or sport stadium.. The number of seats varies pretty much the same as in any O2 Arena, 9500 to 12000... But it is indeed Openair - he was never in Germany so late the last tours.
Would be cool to know if he plays in Hamburg at the Stadtpark again - pretty nice venue, would love to see him there again... remember 1996 the rain concert...
LE