Descend, if you dare, into the deep and (sometimes) stinking depths of Paris's sewers. For centuries, the main source of drinking water in Paris was the Seine, which was also the main sewer. Construction of an underground sewerage system began at the time of Napoleon; and today you can admire the engineering in this fascinating working museum. The Egouts de Paris is part of the city's 2,100km (1,305-mile) system. As you walk through, look out for tunnels marked with a replica of the street sign above. The Egouts can be closed after periods of heavy rain.
Napoleon's tomb, inside the Dome Church, is the crowd magnet here; but while in Les Invalides (a former hospital complex commissioned by Louis XIV for wounded soldiers) don't miss the Musée de l'Armée, Paris's military museum, which contains one of Europe's largest collections of weaponry. Once that's done, leave the coach loads behind and check out 'real' Paris, courtesy of our insider's guide to the Invalides area.
Click here for more information on Les Invalides.