In the first dungeon there are 6 gravestones, from top to bottom in 3 groups of 2. Two in the north, two in southeast corner and another two in between(1 is south of the fairy statue and the other is a little to the west before the guy in green shirt).
Just stand next to a gravestone and press A to fight a ghost. Don't kill the ghosts but surrender to them by pressing D, once for each ghost. If you have Sexy Pants item on, you don't lose health, only 1 stamina point.
After finishing the quest, ghosts respawn at gravestone and can be fought as many times you feel like(it's one of the small exploits of the game).