Visitors to the Serralves Foundation in Portugal’s coastal city of Porto can now experience one of the country’s most celebrated cultural institutions from a whole new vantage point. The most recent addition to the 44-acre park—which counts the Art Deco Serralves Villa and the Alvaro Siza–designed Museum of Contemporary Art among its many attractions—the Treetop Walkway is an elevated boardwalk designed by Carlos Castanheira Architects that winds along an 820-foot-long circuit within a towering canopy of cedars and sequoia.