The phrase "main foyer" refers to the entrance area or lobby of a building, typically the largest or most important one. It is where people enter the building and often serves as a gathering space before reaching other areas inside. Full definition
There was plenty of entertainment in the evenings, a singer in the main foyer / bar area and a show each night in the showroom. (havebabywilltravel.com)
Take, for example, the four beautiful chandeliers hanging in the main foyer illuminated by a whopping 600 bulbs. (sheddaquarium.org)
There is a bar in the main foyer giving you a perfect opportunity to get to know each other a little better. (eharmony.co.uk)