The bottom of the funnel was about 250 feet in circuit, so that the gentle slope allowed its lower brim to be reached without much difficulty.

Involuntarily I compared the whole crater to an enormous erected mortar, and the comparison put me in a terrible fright.
"What madness," I thought, "to go down into a mortar, perhaps a loaded mortar, to be shot up into the air at a moment's notice!" But I did not try to back out of it.

Hans with perfect coolness resumed the lead, and I followed him without a word.
In order to facilitate the descent, Hans wound his way down the cone by a spiral path.

Our route lay amidst eruptive rocks, some of which, shaken out of their loosened beds, rushed bounding down the abyss, and in their fall awoke echoes remarkable for their loud and well-defined sharpness.
In certain parts of the cone there were glaciers.

Here Hans advanced only with extreme precaution, sounding his way with his iron-pointed pole, to discover any crevasses in it.