I have been doing some research for the upcoming trip to Switzerland and the pile dwellings WHS is quite dissapointing when it comes to visiting. The statement on the Palafittes website posted by Walter says enough:
"The sites are actually invisible as they are either located under water or covered by layers of sediment on dry land. This basically impedes the presentation of the original cultural goods.
Numerous special exhibitions, museums, private collections and archaeological parks, however, exhibit finds and show reconstructions of wetland settlements that excellently convey the extraordinary value of prehistoric pile dwellings."
"After all, the pile dwellings cannot be seen?
It is really quite irrelevant to the UNESCO label, whether an object is visible or not. In fact, the pile dwelling sites would be the first world heritage sites submerged in water, which increases the chances of a successful candidature.
While it is important to promote public awareness of pile dwelling sites as a cultural heritage, for instance in museums, the scientific potential of the pile dwellings and their significance with regard to our history and culture are more important than ideal marketing opportunities."
I was planning on visiting the Laténium (looks like the only resonable place in Switzerland on this subject), the nearby menhirs at Corcelles-près-Concise (okay, no pile dwellings, but at least something original to see), maybe the Historisches Museum im Schloss Arbon and the Pfahlbaumuseum at Uhldingen-Mühlhofen (Germany).
For as far as I found out you're not able to see original piles (although they suggest it on pictures on the website with shine-through lakes, but apperently that's not possible to see as an ordinary visitor), but some museums have original artifcats so I guess it still counts as a visit ;-)
Most museums (including Laténium Els) listed on the website also show the travelling exhibition "Der See erzählt"