To find the friendly ghost, walk through the secret tunnel, go past the creepy portraits without looking at them, and climb up the spiral staircase to the attic.

through is used for movement from one end of an enclosed space (like a tunnel) to the other.

past is a preposition meaning to go further than a specific point. ("Passed" is the past tense of the verb "pass," not a preposition!)

up indicates movement to a higher position, which is perfect for stairs.