You can't destroy decor permanent items on the map that you can't move like mailboxes, unmovable basins, beer casks, depot boxes. To add, you can't destroy corpses from a player with a disintegrate rune but you can destruct corpses from creatures or human bodies that aren't from players. You also can't destruct items from the Tibia Store of course. I'm not aware of any other items that aren't indestructible, I've tried numerous things from God Flowers to Parcels.