Max Planck Institut für extraterrestrische Forchung, GRAVITY webpages.
L'Observatoire de Paris - LESIA
I. Physikalisches Institut, University of Cologne
Laboratory for Systems, Instrumentation and Modeling, University of Lisbon
Laboratoire d'Astrophysique de Grenoble, LAOG
European Southern Observatory

An excellent tutorial about (stellar) interferometry with the VLTI can be here.