The Secret Stairs
Talk to the Dwarf Vestri or Austri and tell him that you want to go down the stairs and that you want to become friends. He will tell you to win a trophy at the Hemenster Fishing Competition and then gives you a pass to get in.
Before going to the fishing competition, head to McGrubor's Wood located west of Seers' Village. To get in, you will need to go to the north end and cross where the 'loose railing' is. Go to the west side of the woods. Find a red vine and use the option 'Check vine' and you should get a Red vine worm. Get about 3 worms and head to the fishing contest.
When you try to go through the gate, Morris will ask you for your competition pass. Show it to him and head in. Go talk to Sinister Stranger and tell him he is a vampire. Pay Bonzo for the competition and then go place the Garlic in the wall pipe next to the vampire. The vampire doesn't like the smell (it's the Garlic) and asks to be moved. Go fish by the pipes and get your carp. Take the carp to Bonzo. Bonzo will congratulate you for winning and give you the trophy.
Wrapping it up
Take the trophy back to the dwarf and...