At this point whichever path you choose know that you will be attacked from behind.

Don't get taken by surprise by the armour by the door. Clean out this room now, break the mirror to open a new path and to get some health. Or save this room for later. You need to return here later.

Make it here and clean out this room for a 1-up.

Locate this secret door. Defeat the armour and get the cross within.

Engage in a heavy battle to conquer the library.

Engage in more heavy battles on your way to this room. Break the mirror to open a new path. Beware more enemies coming from the south.

Kill most of the guards in this room by blowing up the barrel. Finish with the rest. Get the brass key.

Find a 1-up behind this secret door.

Continue.