"Beneath the sidewalk, a beach!"
The Situationists are certainly right about that, and the tide is coming in quickly if measurements of rising sea levels are to be believed. The city's grimy boulevards will become suntan lotion splattered boardwalks. You will be able to go whale watching along Main Street and hail a speed boat to take you uptown. Municipalities will replace street lamps with palm trees to make their stretch of waterfront more tourist friendly.
Meanwhile, I've recently returned from vacationing at a fancy island resort where it's more a case of "beneath the beach, the sidewalk."
The coastline was discreetly landscaped into a luxurious simulacrum of tropical Paradise meets the Harvard Club. Each morning, flip-flop clad plowmen raked the sand clear of debris and seaweed. I'm pretty sure he changed into snorkelling gear and, armed with an aqua-broom rather than a spear gun, swept the coral reefs clean as well. From my well-appointed, umbrella-shaded sun lounger, all the comforts of modern life were but a snap of my fingers away. It was the sort of place where NYSE stock tickers ran around the Tiki Bar roof.
City turns into seaside and seaside turns into city, so prepare yourself for "Beneath the waves, a parking space!"