I'm in the tomb at Monfaucon, I've put the lens into the statue and found the burning man, talked to the priest and got the chalice, picked out the bible verses, and the clues section says "go to Spain." But when I go to the "airport", Paris is the only thing highlighted in the choices.

I've tried just solving the lens puzzle and going to Spain without talking to the priest or checking out the tomb (the help text says to do it), but that doesn't work either. What am I not doing?

Have you talked to your rival for Nico's affections on the subject of the chalice?
There should be another place to visit in Paris prior to jetting off to Spain for a second time

I visited the Museum and Nico's apartment. When I tried to show the chalice to Lobineau, the game told me "that is not a good idea." Spain is still blocked.

I'm in the same situation as you are, and I've tried everything I can think of to figure it out.

I did too, everything short of starting over. Then I abandoned the "director's cut" and went back to the original version. As far as I can tell the last thing that's new in the DC is Nicole's "I can't tell" monologue, which happens long before this, so you won't miss anything if you play the older game -- and the original is much better by all accounts (including mine).

ATTENTION! I figured it out.

After shining up the chalice and discovering the puzzle with the stained glass window, talk to the priest about the now shiny chalice. Then go to the Templar tomb at the far corner of the church. There you will discover the family crest matching the one on the chalice. You will be taken into another puzzle. After figuring it out and going back to talk to Nico, you can FINALLY head to Spain.

To unlock the "return" trip to Spain, you first need to use the chalice to solve a puzzle at the Baphomet dig site in Paris.