[Questing for JUSTICE!]

Post-explosion, Sir Percival has a distinctly panicked look to his eyes, alternating between staring at Harold in disbelief, and staring at the pathway in a mixture of shock and terror.

The MERCs may get the feeling that this is a distressingly normal occurrence for people in the presence of Harold, who mostly just looks confused.

And then Wren throws a knife at the cube.

...

"Ow!" the cube exclaims in a rather eccentric masculine voice, as it's struck by the knife."Ah, hello down there! Do you mind awfully not throwing any more things at me?" It asks, rotating 45 degrees anticlockwise in a manner mimicking someone tilting their head to one side.

Cantata's suggestion certainly has merit. The fort has been designed to only allow the one easy way up, a rather daunting cliff-face making any attempt to approach the rear quite challenging for, say, an approaching army, but nothing insurmountable for a few adventurers, particularly if they have some rope or other means of aiding the climb. The stone structure of the fort looks to be several storeys high, and there's only arrow slits at ground level, but larger windows that may serve as an alternate means of entrance are visible on the higher floors.