The House under the Sea by Max Pemberton

I was the first to be out on the rock, but Peter Bligh was close upon my heels, and, wonderful to tell, the Italian almost as quick as any of us. To what gate of the sea the staircase was carrying me I knew no more than the others. The time was gone by when anything in Czerny's house could surprise me; and when at the stairs' head we found that which looked for all the world like a great port-hole with a swing door of steel to shut it, I climbed through it without hesitation, and so stood in God's fresh air for the first time for nearly three days.

That this was the main gate to the sea I had all along surmised, and now proved surely. No sooner was I through the door than all the world seemed to spread out again before my eyes -- the distant island, the shimmering sea, the blue sky shut to us through such long hours. The rock itself, where we gained foothold, lifted itself clear and dry above the breakers at my feet. There were steps leading down to the water's edge, a still pool wherein boats were warped, other crags of the reef defying the tides; these and the silence of the night everywhere; but of men I saw nothing. The bloody fight we had anticipated, blow for blow, and ringing alarm, the struggle for foothold on the rock, the challenge to Czerny's men -- such things did not befall. We stood unchallenged on the plateau, and we stood alone.