At PVG or SHA, stay airside—both airports are large with strong amenities, and security plus distance rule out short exits.
From SHA: Metro Line 10 to Jing'an Temple or Laowai Jie area in 30 minutes (CNY 5). The Jing'an area has good cafes, the Jing'an Temple (CNY 50 entry), and walkable streets. From PVG: the round trip to the Bund takes 110 to 130 minutes leaving very little usable time; consider staying close to Longyang Road area instead. Allow 2 hours departure buffer for re-entry security.
From PVG: take the Maglev (CNY 50, 7.5 min) to Longyang Road, then Metro Line 2 to People's Square or Nanjing East Road in 50 minutes. Walk the Bund riverfront (free), cross to Lujiazui by ferry (CNY 2), and head back via metro. From SHA: French Concession (get off at Changshu Road on Line 7) has tree-lined streets, brunch spots, and boutiques. Budget CNY 80 to 120 ($11 to $17) for a sit-down meal in either area.
Add Tianzifang (arts alley off Taikang Road, Metro Dapuqiao on Line 9) to a Bund visit: it takes 20 minutes from the Bund by metro and covers a full afternoon. A Huangpu River cruise (CNY 80 to 120, 1 hour) departs from the Bund promenade and gives skyline views of both sides. Xintiandi (shikumen stone gate houses) is another 10-minute walk from Tianzifang.