Add to that a flower box holder "Blumenkastenhalterung" to attach said ladder to the balcony securely and you're all set.

Flower box holders can be found in any garden center/DIY store like Migros Do It+Garden, Coop Bau+Hobby, Jumbo, Obi, Landi etc.

Oh, and put a stool on the balcony where the ladder ends, makes for less base jumps should Slinky miss the jump onto the ladder to get down.