Martti Lahti has kindly sent through some more information on The Devil's Nest, including more accurate co-ordinates (page updated).
A link to the Jalasjärven Nature Association web site describes the formation of the cavity (click on the link and press 'translate this page' to read it in English), although I understand there is an ongoing debate as to whether The Devil's Nest is actually a feature of glaciation or a rare underground water or gas opening.
Martti also tells us that there are excellent facilities for visitors to this site, including a spiral staircase to the bottom of the cavity, a high observation platform and a cafe which is open during summer months.
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