If you arrive by plane at the Lyon Saint Exupéry airport, take the tramway "RhôneExpress" to the city from the airport train station. In the city it stops at the railway station "La Part Dieu". There is a tram every 15 mn. It reaches the city in 30mn. You can buy the ticket inside the tram.
Coming to Lyon by train, the simplest is to stop at "La Part Dieu" station.
From the train station La Part Dieu, to reach ENS you should
take the metro line B direction
"Gerland" and stop at the stop
"Debourg" (last before the end of the metro line).
Take the exit with is on the FRONT side of the train (the exit on the
rear side is marked ENS, but it leads to the other site of Ecole Normale
Superieure, for Literature and Humanities, not ENS Sciences).
When you leave the metro station, walk on the side walk in the same
direction until the first cross road (traffic light). Take the street
to the right (called rue Challemel-Lacour), and then it is
straight. You cross a street and a small square (called Place des
Pavillons) and keeping the same direction you enter a pedestrian
street called "Allée d'Italie", in which you will find ENS, after a
small square with a fountain in the center (see the map below).
From the train station the metro needs less than 10mn to reach the
station Debourg, and from the station, it is about a 7-8 mn walk to
reach ENS.
When you arrive at ENS take the entrance of the left side of Allée
d'Italie, which is the main entrance. The entrance is locked but the
person at the entrance desk can unlock the door for you if you knock
at the door. If you arrive late, or if the person at the entrance desk
does not see you, you may have to call the number indicated at the
door with the interphone which is at the entrance door.