Join us as we explain the wildest, weirdest, most shocking moments of all time in History Countdown - histv.co/countdown Dublin, Ireland is much more than a city full of pubs and pints. Pagan burial tombs, subterranean defense tunnels, and mysterious burial crypts line the underground below the rolling hills. Find out more in Season 2, Episode 4, "Viking Underground." #CitiesoftheUnderworld Subscribe for more from Cities of the Underworld and other great The HISTORY Channel shows: histv.co/SubscribeHistoryYT Check out exclusive The HISTORY Channel content: History Newsletter - histv.co/newsletter Website - histv.co/History Facebook - histv.co/Facebook Twitter - histv.co/Twitter "Cities of the Underworld" descends below the streets of major cities such as New York, Cairo, London, and Tokyo to explore the remnants of subterranean civilizations left buried there. HISTORY® is the leading destination for award-winning original series and specials that connect viewers with history in an informative, immersive, and entertaining manner across all platforms. The network's all-original programming slate features a roster of hit series, premium documentaries, and scripted event programming.