Yes, that's an amphitheater outside the mission. The other building in question is the giftshop, Museum and theater, which shows a film on the mission and mission life every hour on the hour.
Great! So they have plays about the mission at the amphitheater? It´s nice to see that they have a museum and a Theater showing a film about the mission. It´s important to have such things, to keep history alive and interesting...
Back in 1958, 50 years ago this coming June, the mission amphi- theater featured a play concerning the Alamo called A CLOUD OF WITNESSES by Ramsey Yelvington. (I just got this old flyer for it in the mail.)
And a concert ticket to watch say, Neil Young, costs much more than three hours salary today! More like eight hours salary - before tax. Neil Young is touring Europe right now and I believe a ticket costs about $150!