Slănic Prahova holds the record for Europe's largest underground room — a single excavated chamber measuring 54 metres high, 32 metres wide, spanning 2,900 square metres at a depth of 208 metres below the Carpathian foothills. Mining began here in 1685 under Habsburg administration, extracting table salt in blocks that were hauled by ox-cart to Bucharest and Brașov. The mine operated continuously until 1971, when industrial extraction shifted to newer sites and the caverns were repurposed for therapeutic tourism. Today the subterranean network encompasses fifteen interconnected galleries, their walls bearing the scalloped tool marks of three centuries of hand-hewn labour. The therapeutic microclimate attracts visitors seeking halotherapy — the air holds a constant 12°C year-round, with humidity near 60 per cent and sodium chloride aerosols that proponents claim benefit respiratory conditions. The main hall houses a permanent underground amphitheatre, a chapel carved entirely from salt, and a small museum displaying mining tools, geological cross-sections, and photographs documenting the site's industrial past. The Unirea Chamber, opened to the public in 1975, features a subterranean lake with rental paddle boats, while the smaller Mihai and Carol galleries exhibit salt stalactites formed by mineral seepage over decades. A slănic salt mine day trip from Bucharest typically combines the mine with a stop at Snagov Monastery, the purported burial site of Vlad III, or routes north through the Prahova Valley toward Carpathian villages. The drive from the capital follows the DN1 highway through Ploiești, passing oil refineries that defined Romania's early-twentieth-century economy. Most guided tours depart Bucharest between 8:00 and 9:00, allowing three hours on-site before returning by late afternoon. The mine's shuttle bus descends 208 metres through a kilometre-long access tunnel — visitors walk the return route, ascending via illuminated ramps that trace the original mining levels. Entrance costs 14 RON at the gate, though many visitors book combined transport and admission through operators offering hotel pickup from Bucharest's central districts. The site closes Mondays; Tuesday through Sunday hours run 09:15 to 15:30, with the final shuttle descent at 15:00. Independent travellers reach Slănic Prahova via intercity bus from Bucharest's Autogara Militari or by private car along the E60 and DJ102K routes, a journey of roughly two hours fifteen minutes.