A Voice in the Dark:
Surprisingly the castle idea reminds me of the Doctor Who episode: Heaven Sent.
I had forgotten about that episode as Capaldi was one of my least favorite Doctors but it is a great idea.
A Voice in the Dark:
Very much sounds like the first MYST game. May want to check if that's something your players want. That game isn't for everyone.
I'm not sure I follow your meaning here... Maybe because I never played MYST but also because the players would know the concept (i.e. - trapped and have to jump into books to escape) before they signed up... What am I missing?
Window Watcher:
Reminds me of the kids' book series "Magic Tree House," cause they'd read books and go to a bunch of time periods, usually bringing something back that would help solve their current problem.
The nostalgia...
Never heard of that series before... Will have to look it up...
Window Watcher:
Possible idea:
They have to gather pieces to assembly a seaworthy boat. The body, the sails, the sextant/compass (navigation), oars, food/drink, shelter, searchlight, etc.
This actually jogged a memory of the Staff of Jericho obelisk device they built in R.I.P.D.