Ice-choked tower, Mondavia, Nanglangka.
In order to activate one of the plans (cant remember the name) you have to sacrifice an Shield-Icon card. If i sacrifice a hero, can i use his sacrifice ability too?
No. You can't sacrifice something twice. You resolve each sacrifice separately.
Spiderling nest says 'Cancel a players card'. Can the invader cancel any card, even for example a very expensive one like the green location with strength 5? And my paid cards are lost?
Yes, to both parts of the question. This is covered near the bottom of page 5.