Gabion walls don't need any kind of drains because they are porous throughout. Gabions can be customized to make them more useful in public spaces. Gabions can be filled with any heavy material--diverse stones, metal artifacts, obtanium, etc.
grout terrace joints with epoxy. This is similar to the joints of cement. However, these joints are waterproof, in contrast to addition of cement which can always suck up water (and may burst in winter).
olive trees in courtyard. Evergreen, soft grey tones, hardy and easily shaped. My husband really wants one of these in our garden so he can have an "on-tap" supply of olives and a reminder of my Italian roots.