Polytechnique is located in a south-west surburb of Paris, between Palaiseau and Orsay, on the Saclay plateau. This map shows how to walk from Lozere to LIX.
The campus is easily reached using the RER B line from Paris, from Orly Airport, and from the Charles de Gaulle Airport. In all cases, take the RER line B in direction of Saint Rémy-lès-Chevreuse until Lozère Station. Move to the other side of the tracks (using the subway or footbridge to cross the railway). There is a café to the left. Go left at the café, then take the (steep) path to Ecole Polytechnique (about 10 to 15 minutes). See this map.
Once you have arrived on the campus, you will need to access the "Labo" section of the buildings. This section is in red below. LIX is in Aisle 0, which is the top most part of the blinking section. Access to this part of the campus is restricted to those with badges. If you don't have a badge, then find a phone (some extrances have phones for this purpose) and contact the person who you plan to meet. They can bring you inside.
1- Reception for visitors with car
6- Reception for visitors from RER
7- RER line B Lozère station (stairs)
The walk from Lozere is steep and some people wish to avoid it. Another way to the campus involves taking the line TransEssonne 91-06, which leaves from Massy-Palaiseau in front of the RER B station. The schedule is here. It's best to exit at the stop 2 "Les Laboratoires", see this map.
``So forget any ideas you've got about lost cities, exotic travel, and digging up the world. We do not follow maps to buried treasure and 'X' never, ever marks the spot.'' Indy in Indiana Jones & The Last Crusade.