Stone Tunnel (5)
================

+-- Level +1 ---------------+
|     <                     |
|      %                    |
|      v                    |
|                           |
+---------------------------+

+-- Ground level -----------+
|                           |
|               *           |
|              /|           |
|             / |           |
|         *--*  *           |
|        /     / \          |
|      ^/     /   \         |
|      %     *     *--*--*  |
|     /      |           |  |
|    /       |           |  |
|   *        *           *  |
|    \       |          /   |
|     \      |         /    |
|      *     %        *     |
|      |    /|v       |     |
|      |   / |        |     |
|      *--*  *     *--*     |
|     /       \   /    \    |
|    /         \ /      \   |
|   *           *        *  |
|    \         /         |  |
|     \       /          |  |
|      *     *--*--*--*--*  |
|      |     |              |
|      |     |              |
|      *--*--*              |
|                           |
+---------------------------+