Alberobello has 1,500+ trulli — whitewashed stone houses with conical grey roofs built without mortar. The theory: the Counts of Conversano ordered dry-stone construction so buildings could be quickly demolished before royal tax inspectors arrived (no mortar = removable roof = "this isn't a permanent building" = no property tax). The reality: probably more practical (local limestone splits into flat slabs perfect for corbelled construction). The UNESCO designation (1996): Rione Monti (the hillside district with 1,000+ trulli) is the largest concentration of dry-stone buildings in Europe.
Rione Monti: The main trulli district — 1,000+ cone-roofed houses on a hillside, connected by stepped alleys. Touristy but spectacular. Many trulli are now shops/restaurants. Rione Aia Piccola: Adjacent district — RESIDENTIAL trulli still inhabited by families. Quieter, more authentic. Trullo Sovrano (€3): The only 2-story trullo, now a museum — see interior furnishings, the cone structure from inside. Chiesa di Sant'Antonio: A CHURCH built as a trullo — the largest cone-roofed building, 1926. Sleep in a trullo: Many converted to vacation rentals/B&Bs (€60-150/night on Booking). The experience: sleeping inside a cone, whitewashed walls, thick stone keeping it cool in summer.
Practical: 1h from Bari (train, €5). Day trip works but overnight in a trullo is the experience. Combine: Ostuni (25 min) + Alberobello + Polignano (35 min) = the Puglia triangle.