Scientists estimate that this world treasure is sinking about  6.4 cm   (2 1 / 2   IN .) per  decade. Flooding is the most urgent problem. A plan to hold back the rising Adriatic with a system of mobile underwater barriers has met with controversy, and at any rate won’t be completed until at least 2011.

Set on 118 separate islands, dredged out of a marshy lagoon and shored up on wooden pylons, Venice floats upon the Adriatic Sea like a mirage. Amsterdam and Bruges and a few other European cities may have a network of canals draining their cityscape, but in  Venice  the  canals  are  the  cityscape—creating land to go with it was an engineering triumph over nature.

Nature,  however,  has  a  way  of  striking back. In the first decade of the 20th century, the  city’s  central  piazza,  St.  Mark’s  Square, flooded less than 10 times a year, but by the 1980s it generally was underwater 40 times a  year.  In  recent  years,  the  problem  has grown even more acute, with as many as 40 floods   between   September   and   March alone.

Unlike other canal cities, Venice has no streets at all, only canals (more than 150 of them) and paved walkways. Motor launches and  anachronistic  black  gondolas  are  the way  to  get  around  town—that  and  walk-ing,  which  usually  means  getting  lost  in  a maze  of  narrow  stone  lanes  and  high-arched bridges. Perplexing as it is, that layout  was  a  matter  of  necessity—buildings were erected wherever land seemed solid enough, while winding channels between the  islands  became  the  major  canals,  like the sinuous Grand Canal, or the unbridged (cross it by ferry) Giudecca channel.

Most  tourists  simply  mill  around  the colonnaded  Piazza  San  Marco—arguably the  loveliest  public  space  in  the  world—and file through the guidebook must-sees: St.  Mark’s  Basilica,  a  glorious  Byzantine church  with  glittering  gold  mosaics;  the iconic Campanile bell-tower; and next to it the exotic Doge’s Palace, with its Arabian Nights  facade.  But  getting  beyond  San Marco  is  essential  to  understand  Venice. Cruise  the  Grand  Canal,  lined  with  Venetian Gothic pallazzi; stroll around the city, popping into obscure churches and browsing  street  markets.  Hop  on  a  vaporetto and  visit  the  outlying  islands—Murano, home  of  exquisite  glass  makers;  Burano, the island of lace makers; or the Lido, Venice’s local beachfront.

Every time I visit Venice, I’m struck by its unique sensory impact, all of it expressing the  watery  essence  of  the  city.  There’s  a constant murmur of water lapping against stone;  the  very  air  feels  magically  moist against  your  skin.  Then  there’s  that  faint scent  of  decay,  a  blend  of  rotting  foundations,   crumbling   plaster,   and   sediment slushing around the canal floors. Somehow it   manages   to   be   intensely   evocative, even magical. It’s the sheer Venice-ness of Venice—and it can never be reproduced.