The site is run by Türkiye's Ministry of Culture and Tourism through the İznik museum directorate. Its listing, checked on October 10, 2026, shows the ticket office closing in the mid-afternoon and an entrance ticket of 3 euros for foreign adults; the welcome center has the museum, a café, a shop and restrooms. Pope Leo XIV took part in an ecumenical prayer service beside these excavations on November 28, 2025, during his journey for the council's 1700th anniversary.
Be careful with one claim. The exact place where the council met is not settled. The archaeologists who excavated the basilica date it to about 380 and connect an earlier wooden church on the site with the council. Eusebius, who was there, writes of the bishops gathered in "a single house of prayer" and of the decisive assembly in "the central building of the palace." The Holy See described the papal event simply as held near the excavations of the ancient Basilica of Saint Neophytos.
A second council met at Nicaea in 787 and defended the veneration of sacred images; the Byzantine church linked with it in the town is now a mosque.
Good to know before you go: İznik is an archaeological site and a small town, not a Catholic shrine, so a group that wants Mass there has to arrange it in advance. It lies southeast of Istanbul across the Sea of Marmara and is reached by road. Hours and prices at Turkish state sites change with the season, so look at the official listing again shortly before you travel.