Open-air lobbies (5)
I believe the answer is:
atria
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">open-air lobbies</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for atria that I've seen before include "Roofed central courts" , "Open courts of Roman houses" , "Open-roofed entrance halls (Roman) - glass-roofed central halls (modern)" , "Apartments" , "Central courts (in ancient Rome or shopping arcades)" .)