You have to collect 20 treasures inside a haunted mansion.
Originally written in 1980 for the Commodore PET.
The C64 versions are much later (unofficial?) ports.
The c64 port distributed by The Guild was called Scary Adventure.
A much later, unofficial port was made for Plus4; see here.
[+] Users currently playing this game
I have to say the last game for the PET from John O'Hare is the best one. Even with the annoying ghost and the lots of black cats you can cross during your adventure. Highly recommended and it was the best one technically speaking too!
You can find the last John O'Hare on zimmers.net : http://www.zimmers.net/anonftp/pub/cbm/pet/games/english/unsorted/pet_games_05.d64.gz