Been in several.
Without a doubt they are bloody horrible.
The only ones accessable are drifts (obviously!) and apart from the odd stretch of mainway they are generally about 4.5 feet high so you can seldom walk upright (many of the working boards are only 18inches high)
Bad air is a huge problem, all of the ones I have been in suffer heavily from it, in one notable case oxygen was down to 10.5% which will kill you. We have been using BA closed circuit breathing apparatus which is very difficult to use in a confined space and gives you a very limited time.
Another problem is that they invariably cut through bad ground and enterances are very poor. One of the ones I've been in meant you had to crawl under some old tubs along the trackway to get through the collpapse at the enterance.
For coal a gas monitor ougth to be seriously considered, the majority of coal seams give off methane and blackdamp is a serious problem. All of the coal mines I have been in relied on some form of forced ventilation when in use, without it the air becomes bad very quiclky!
I have only found one with reasonable air quality and that was the one that you had to crawl under the tubs :blink:
I have been searching for a long time for a pleasant coal mine to wander through and have yet to find one that isn't a nightmare 😢
Infact, everyone that I have been into is so dubious safety wise I would think long and hard about telling anybody how to get in! If you find one that is livable then give me a shout!