A recent question about the Lille Citadelle reminded me of my travels in Italy a decade ago where I was wandering around the outskirts of Alessandria and found a huge old citadel that was seemingly neglected and still in use by the military.
It turns out that the Citadel of Alessandria is listed by UNESCO but I can't find any information about whether tourists can visit it these days.
It has a homepage in Italian only which doesn't mention visiting. Wikipedia barely mentions it and Wikitravel and TripAdvisor don't mention it at all.
Another site which also seems to be a homepage contains lots of photos, including at least one which looks like a tourist entrance and at least one other which looks it precludes civilians from entering.
So are there any options to visit this citadel as of 2012?