The other day I came across an American-style door knob at a local restaurant. Czech door knobs don't turn. I loved the picture they posted showing how to turn the knob to open the door.
Most doors have knobs that don't actually turn the latch. The knob is basically just a prop to move the door as you lock and unlock the door.
It's a good rule to not keep the key in the inside lock. If a key is in the inside lock then you can't open the door from the outside. The key won't fit in the outside lock if there is a key in the inside lock. I know people who've had to call a locksmith because a flat mate left a key in the inside lock and fell asleep. Calling a locksmith will run any where from 700 Kč to 1000 Kč (~$35 to $50).