The last time I looked for the source of the magical radiation, I accidentally discovered an underground passage. Unfortunately, my Mecha malfunctioned. I had to resort to human strength - or lack thereof - and I couldn't pry it open.
Legend has it that the Dead Key has mysterious powers, and can open any magic seal. That's the only way we'll get to the underground city. So, will you help me out?
Perhaps this gate won't open because it's been magically sealed.
After all this hard work, I still can't get the door open... it's pretty disspiriting. But I suppose we at least know where the main door is. We should definitely be able to get it open within the next decade or two...