The Coach-a-Bowers is a coach driven by the Dullahan. It is pulled by four headless horses. It was used to take Valkyrie to Nye to seal her True Name in Mortal Coil. It first makes an appearance when an unnamed woman is dragged inside it after hearing a banshee's scream.
Once entering the Coach-a-Bowers you die and, in Valkyrie's case, you can come back to life by leaving the coach.