A network of tunnels in the hill north of town, presented by their excavators as part of the same supposed ancient pyramid complex. Mainstream archaeologists consider them most likely a medieval or post-medieval mine. Either way, the kilometre or so that has been opened up is genuinely atmospheric — narrow, cool, lit by string lights, with crystal-laden chambers and underground "meditation rooms".
Tours run from the entrance pavilion every hour. Hard hats are provided. Bring something warm; the temperature underground is around 12°C year round.