Which game is this?

OK, I am stumped. Many years ago, my cousin had an MSX machine, and we spent many many hours playing this one game, whose title escapes me. The setting was a castle (no, it doesn't look like the Castle/Castle Excellent game from what I recall), and you had this little guy in armor and wielding a sword running around fighting monsters. There might have been some sort of keys involved that you had to find as well. The scenery was very grey-ish.. it had a lot of levels and was highly addictive. Any idea what game this might have been? Would love to find a copy for a nostalgia trip.