Tunnel Vision

You can call me a smartarse for putting this in waterscapes - but it does say the water can be flowing or standing, so I'm going to assume that frozen counts too.

I'd really like some constructive feedback on this piece. Since the pic needs to be fairly high-contrast in order to stand out, I thought about doing some very mild manipulation - I've touched up the existing image very little. Any tips from the really great photographers out there at all?

For anybody interested in the shot, it was taken under the Franz Josef Glacier in New Zealand, and the tunnel here was big enough to crawl through. I just loved the way the ice darkened towards the centre of the tunnel, and the way the folding sheets of ice to the sides gives the picture an abstract feel. Hope you like it!