An underground tunnel with a truck on the track. Wood engraving, 1868. https://www.rawpixel.com/image/13954724/underground-tunnel-with-truck-the-track-wood-engraving-1868Free Image from public domain licenseWorkmen fitting the metal casings for an underground tunnel. Wood engraving, 1868. https://www.rawpixel.com/image/14002235/image-cartoon-person-crossFree Image from public domain licenseUnderground tunnel illustration vector https://www.rawpixel.com/image/573140/underground-tunnel-workersView licenseA trial journey on the first part of the underground railway in London. Wood engraving, 1862. https://www.rawpixel.com/image/13978771/image-person-baseball-clothingFree Image from public domain licenseUnderground tunnel from Underground, or Life Below the Surface. Incidents and Anecdotes Beyond the Light of Day, Startling… https://www.rawpixel.com/image/571487/underground-tunnel-workersFree Image from public domain license