Sure
So you leave the airport direction "Cascais" or "Sintra".
-You will be in a main road know as "2ª Circular".
Know in "2ª Circular" (you are going to make some km in this road) use the exit that says "A5 Cascais"
After this Exit - You are going to a small freeway know as "CRIL"
Just follow the indications for "A5" direction "Cascais".
In A5 you´ll make a hill climbing, and after the hill (you´ll be able to see the game site on your left in the middle of the valley) use the Exit that, says "Estádio Nacional" or "Jamor", it is the 2nd Exit after you get in the A5.
***In this Exit you have got to make a left turn, as you leave A5.
After this Exit and passing thru a tunnel under A5 turn to your first left option to a parking lot area with a´lot of trees (after some small road bumps). And you are in the game site.
Hope this helps
See you here.
Cheers
Jaime Menino
P.S. By the way just to keep on topic, know (22h21) it´s heavy raining, and I live near the game site.