Aw, sad. I read that story as a kid and thought it was hilarious.
This is the problem with history; sometimes you learn marvelous new things you never knew, and sometimes you end up deflating the marvelous things you thought you knew.
I believe this one actually happened.
Godesberg was located atop a mountain, possessed a strong curtain wall, and had turned all possible approaches into a deadly kill zone, but was an old medieval castle at a time when everyone was switching to star forts, so it was expected cannonfire would be able to take it down. In practice the castle was so high up on the mountain, the besiegers had to elevate their guns to shoot against gravity which just caused the cannonballs to fall back to the earth and ended up having their own guns destroyed (by counterfire, not by their own shots). After burning through a ton of gunpowder, they finally discovered the problem and repositioned the cannons to hit the walls straight on rather than at an angle, which managed to breach it.
At that point the formidable curtain wall was breached with a huge hole in it but when the besiegers prepared to send troops to take the breach they remembered that the defenders had guns and cannons too, which would cut them up in the killing zone before they could even reach the wall. So they ended up just leaving the hole there without doing anything.
With artillery and assault ruled as failures, they decided next to dig a sap under the wall, fill it up with the remaining gunpowder and blow the castle up from beneath, before sending the infantry through the trench to take the fort. This meant they had to dig through the solid rock of the mountain, but eventually it worked and sent half the fortress flying into the sky. Except the chunks of the wall started landing on the trench the soldiers were trying to move into, so the attackers were forced to abandon the trench and do an overland assault. Which involved running straight into the kill zone they were trying to avoid and predictably they got cut up trying to take the breach.
At that point, the besiegers got quite sick of things and resorted to the old toilet shaft stratagem, which finally took the castle. After all the grief Godesberg had been given them, they might have figured at that point even that hell would have been better than enduring another month of trench warfare.