Museums and historical sites have a fairly universal etiquette, with local additions worth checking at the door. The universals: keep your voice low, do not touch artifacts or carvings, obey photography signs since flash genuinely damages pigments and textiles, do not eat inside, and never climb on ruins or monuments for photos. At sites that double as active religious spaces, which is common across Asia and the Middle East, add modest dress, shoe removal where indicated, and silence during prayers or rituals.
Some countries add their own layers: separate entrances or dress rules for sacred areas, restrictions on visiting during ceremonies, or requirements to hire an official guide at protected sites. Signs at the entrance usually spell these out, and staff will politely enforce them.
To actually learn rather than just look, a licensed local guide or the site's audio guide is worth the modest cost, since context turns stones into stories. Going early beats crowds and heat, and reading even a paragraph of background beforehand changes what you notice. Guest books and donation boxes at smaller sites are appreciated ways to give back.