As far as churches go, this one has to be up there with the most unusual ones, actually it's up there with the most unusual buildings full stop and an absolute MUST for every Brutalist lover.
Designed in 1968 by architect Hans Buchmann and sculptor Josef Rikus together with theologist Wilhelm Nyssen, Johannes XXIII church is based on a depiction of the Tree of Jesse (no, me neither). The sculptoral outside is continued on the inside in concrete as well as wood. It's so unusual that I have one picture from the inside where in all honesty I can't figure out if I have put it on here upside down or on its side. I just can't work it out.
Below are a few more pictures from the outside and some from the inside, including the possible upside down one. 
Kirche Johannes XXIII, Berrenrather Str. 127, 50937 Köln