A low circular glass building by SANAA with no front and no back, holding Leandro Erlich's Swimming Pool, where people appear to stand underwater. One practical warning that most guides get wrong: the underground half of the pool is booked SAME DAY ONLY, from 09:00, online or at the desk, and you need a paid ticket to match. Viewing it from the courtyard above is free. Note it closes for renovation from May 2027.