Walk up to the Zealot, tell him that you do not have someone that you follow and he will tell you about the secret cave and the Salve amulet. Alternatively, tell him that you follow Saradomin or Guthix and he will still tell you about the secret cave and the Salve amulet. He has a key, but won't trust it to anyone else, pickpocket the Zealot's key from the Zealot for later use. You might want to use the drop trick to obtain more than one key, in case you lose it. Just south of the Zealot there's a cart track with two carts. Climb over the first, walk past the second and enter the cave.