Interesting points. I agree there's a little trend between T2 FMs "improving" or evolving gameplay and level design, while T1's lean on the retro style. Examples of each: What Feast of Pilgrims is to Life of the Party, and what Intertheft/this FM/Lost Among the Forsaken are to the original T1 design...
Or is it?
Are we attribuing too much to single, standalone FMs in both cases? I'm not sure where the line is. I'm more doubtful in T2's case, not so much on T1.
Ultimately the answer a...
I assume you are asking about A Mountain to Climb, mission 5 of the campaign. At the beginning of this mission, the player needs to find another way into the mountain castle, because the other side of the drawbridge is up.
On the right of the gargoyle statue on the east side, there is a hole in the railing of the accessible side of the drawbridge. Let yourself fall down onto the rock platform below and continue to the mountain castle from there. A glowing crystal lights the way.
Otherwise a solid mission that belies its age (though key-heavy) but the vault key solution is really terrible and utterly non-divinable on one's own, especially as the script seems to be broken in some way without clarity as to what actually triggers it - I just fuddled with all inventory in front of the ghost for minutes on end until I got a response.