Is ONE PIECE episode 174 filler?
Canon No, episode 174 of ONE PIECE is canon.
#174
A Mystical City! The Grand Ruins of Shandora!
幻の都！雄大なるシャンドラの遺跡！！
Aired 16 Nov 2003
Mochibayo compiled this list from MyAnimeList's labels, because MyAnimeList's episode data is not reaching us at the moment.