If you're going to do sightseeing, a short walk to the Vadstena lighthouse is definitely interesting. You see the town from a completely different angle. Directly at the lighthouse, a surrounding bench invites you to take a break. A staircase helps you get back onto the pier after jumping into the water.
Even if it is a "dead end" way, it is still worth seeing the town from the water side. At the lighthouse, a bench invites you to take a stretching break.