Pictured: The world's longest underground slide, which is hidden inside a MOUNTAIN in Graz in Austria
By Jessica Hamilton Published: 09:42 EDT, 14 May 2024 | Updated: 09:42 EDT, 14 May 2024 Thrillseekers - grab your ticket... to slide. This is the highest underground slide in the world - and the second-highest overall - a structure that is a staggering …