Excursion underground   - lasts about 1-1,5 hours   - groups are required to make a reservation   - individual guests are formed into groups and they can get   underground on the hour   After the first contact we recommend groups to make a written confirmation (student groups make a name list of the students) about the arrival and wishes.   We kindly ask groups which have reserved beforehand an acquainting in the museum to confirm their time of arrival and group size by phone.   GROUPS CLOTHING DURATION PROGRAM OF AN EXCURSION   The guide of the mining museum holds himself all rights to change the timetable and routes underground to guarantee a safe visit.