Several watch-towers guard the entrance to Goblin-town, preventing an easy infiltration. They will need to be brought down before you can enter safely.
'If you are going to get inside Goblin-town unseen, you will have to deal with the watch-towers between here and the Gate. I have heard from the scouts that they seem to have been assembled in a hurry; they must be expecting an attack from the Great Goblin. Luckily for us, hasty construction oft means hasty destruction!'
Goblin watch-towers have been erected between Vegbár and Goblin-town.
You should destroy goblin watch-towers so you can enter Goblin-town unnoticed.
You destroyed some of the hastily-erected watch-towers.