You can reach the LLR laboratory easily from Paris, by taking RER B up to Massy-Palaiseau and then a bus (91.06B or 91.06C) up to Polytechnique Lozère bus station. From the center of Paris this will take about 45 minutes up to Massy-Palaiseau + 10minutes by bus + 5minutes by foot.
Otherwise, the most athletic among you can take the RER B up to Lozère stop and then climb the stairs up to the Ecole Polytechnique (here a nice video showing the way https://www.youtube.com/watch?v=OoeTfrHLrxw). In this case you should considere ~45minutes from the center of Paris up to Lozère + 20 minutes by foot.
Here some more informations about how to reach LLR and Ecole Polytechnique
https://www.polytechnique.edu/en/maps-and-directions
You can find some detailed maps above (click on "Posters" button).
For the accommodation, you have three possibilities:
1. either book an hotel in Paris, close to any RER B stops (and then reach the LLR by RER B + bus/stairs)
2. or book an hotel directly in Massy, close to the TGV train station (and then reach the lab directly by bus or by RER B + stairs)
3. book an hotel in Orsay or Palaiseau (and then reach the lab, by RER B + stairs) Second option is the most comfortable (but not necessary the cheapest).
Here you can find a list of hotel close to the Ecole Polytechnique
http://llr.in2p3.fr/IMG/pdf/liste_des_hotels_site_web.pdf
And here a list of hotel close to Massy TGV station:
http://www.booking.com/hotel/fr/kyriad-massy.fr.html
http://www.booking.com/hotel/fr/sejours-amp-affaires-massy-atlantis.fr.html
http://www.booking.com/hotel/fr/adagio-access-paris-massy-gare.fr.html
http://www.booking.com/hotel/fr/residence-paris-massy.fr.html
The social diner will be on December 1st 2016, at restaurant "Nos ancêtres les Gaulois". Look at the map below :
39 Rue Saint-Louis en l'Île, 75004 Paris
