most (not all, some contributions are QTVR-only due to historical reasons)
many, but depends on photographer's choice of file upload (newer event = more likely to work) and your device's capabilities. You may experience slow playback, distorted images or unexpected browser quitting if there is only limited memory/GPU power available.
This coal mine exists since 1908 (formerly known as 'Andaluzja'). The water
management chamber, located at 300 m below ground surface is not used
anymore (only levels 451 and 635 are operating). The water management
served to supply water for technical and emergency purposes.
Special thanks for the help with creating this panorama to Management of the coal mine: Mr. M. Majcher,
Mr. W. Bugajczyk (with me below ground) and Mr. M Sitko.