We had a brilliant visit to this place. It far surpassed our expectations and we highly recommend it. Our guide was excellent, very informative and interesting. The tour included going outside and visiting other places which was a fantastic bonus. We thoroughly enjoyed it and we consider it excellent value for money. We paid €15 entry which included the guide. It lasted about 90 minutes, a lot was packed in in that time. Do not take a massive bag as some of the tunnels are VERY narrow. Probably not great if you're claustrophobic although escape routes were offered in the very narrow parts.
The only downside was two very horrible, aggressive and rude women outside dealing with the patient visitors trying to work out how to get in and what was going on. Totally uncalled for and almost put us off of going in. Apart from them it was great!