Yes, you can go topless at Lido di Ostia, but it depends strictly on where you set your towel.
While topless sunbathing is generally acceptable, doing so on the main, heavily populated family beaches is uncommon and can attract unwanted attention.
For a comfortable and designated topless/nude experience, head to Oasi Naturista Capocotta. Location: Located along the Via Litoranea (around km 9.4) just south of Lido di Ostia. The Atmosphere: This protected nature reserve is officially recognized as a naturist/clothing-optional area. Sunbathing topless or completely naked is the norm here. Facilities: Unlike many secluded nude spots, this beach features amenities including sunbed/umbrella rentals, a bar, and a restaurant.
How to access: You can take local bus services to the beach or drive and park along the roadside. Once at the access paths, look for Varco 3 (often frequented by the LGBT community) or Varco 4, which leads directly into the naturist area.
