Spodek is a multipurpose arena complex in center of Katowice. It was opened in 1971. It was designed by Maciej Gintowit i Maciej Krasiński. It's one of first buildings in the world employing the principle of tensegrity. Estimated cost of Spodek was 200 mln zł, but finally it was 800 mln. Right now in the complex we can find icerink, gym, hotel and two indoor arenas.
In Spodek took place some big music concerts (groups like Metallica, Judas Priest, Deep Purple, Depeche Mode, Alice in Chains). From regular events most known are Metalmania, Mayday Festival, Rawa Blues Festival, Odjazdy, Mystic Festival.
From bigger sports events there were organised World Championship in ice hockey, European Basketball Championship, European Woman's Volleyball Championship, World Championship in Volleyball and European Handball Championship.
I recommend visiting this cache by night, because is much less people there, so cache is safer (remember, it's city center!), and Spodek looks wonderful with colorful lights :)