Volary

Well done! You've disclosed the first two clues. But you are still in. Besides, you've dropped unexpectedly in the Volary. You know, my master was a hight engineering. He built machine, war machine, kitchen machine, machine for flying, and many others Automata. So that to overcome this third challenge, and find out the clue, you have to detect "the letter combination" that the cheeky Spirit has hidden, again, in the crossword below. Once you've found it, please go back to the Hall and write it in the lock.