ðɪs ɪz bɪkˈʌz ɪt hˈæzbiːn ɐ mˈaɪnɪŋ sˈɛntɚ fɹʌm pɹˈiːɹˈoʊmən tˈaɪmz, æz wˈɛl æz hˌævɪŋ ɐn ˈɪntɹɛstɪŋ sˌʌbtɪɹˈeɪniən stɹˈʌktʃɚ.
This is because it has been a mining centre from pre-Roman times, as well as having an interesting subterranean structure.