Hmm, that seems unlikely but I honestly don’t know. Possibly free for US citizens but a small fee for visitors? I can’t imagine it would be closed to visitors, though you should be able to contact them to find out.

The talk I so enjoyed is on YouTube with many others: https://youtu.be/AvqtY_7Q7hI?list=PLEA69BE43AA9F7E68 (video 30 is MacKaye)