1 - <a href="https://en.wikipedia.org/wiki/base_tunnel" class="extiw" title="en:base tunnel">base tunnel</a>, 2 - intermediate tunnel, 3 - top tunnel, 4 - open recess, 5, 6, 7 - tunnel approaches, 8 - recess approach
<a href="//commons.wikimedia.org/wiki/User:Leon_II" title="User:Leon II">Leon II</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>