What you find differs from place to place. Ephesus, the agora of ancient Smyrna in the middle of İzmir, the acropolis of Pergamum, Sardis and Laodicea are excavated archaeological sites; at Laodicea the excavations have uncovered early churches. Thyatira and Philadelphia lie under living towns, so what remains is modest: scattered ruins in Akhisar, and in Alaşehir the standing pillars of a church of St. John. Türkiye's Ministry of Culture and Tourism runs the main sites and publishes their current hours and ticket prices.
Revelation places John on Patmos when he received the vision (Revelation 1:9), an island in the Aegean some fifty miles (80 km) from Ephesus. The cave and monastery venerated there are in Greek Orthodox care. Ephesus is the best known of the seven: ancient tradition, recalled by Benedict XVI in 2006, says John worked there for many years, and the Council of 431 met there.
Good to know before you go: expect ancient cities and Scripture rather than shrines with a daily liturgical life. The Basilica of St. John at Selçuk, for example, is a ruin, not a functioning church. Where and whether Mass can be celebrated has to be arranged for each group, and entry requirements for Türkiye change, so check both for your dates. What the places offer is specific: each letter of Revelation 2-3 can be read in the city it was sent to. They are not the Seven Churches of Rome, which is a walking devotion among Roman basilicas.