The event page on facebook says:
There has never been something like this in Hamra.Some people are guessing a public library, a theater or a cinema, free parking, a concert, etc... What do you think it is?
You will definitely want to experience it...
HINT #1: There's no entrance fee
HINT #2: It's not outdoors
HINT #3: It's a nocturnal activity
Update: HINT #4: "Many of you expressed very valid hopes and wishes we all share for our home, cocoon, first and last love; our Hamra. But seriously, who'd campaign for parks/freedom of speech/benches/free parking/public bathrooms/etc etc... with an event on a Saturday night that starts at 10:00 pm and ends at 6:00 am Sunday morning? That was clear from the start, and we make no apologies to the misled. We all want our Hamra to be a constantly improving place. We can and will do our utmost to achieve that, but that won't stop us from having a lot of fun in the meantime. In Hamra!"
Meh. It seems like a lame concert. I was hoping for something much better. Marketing #Fail