You're not, by any chance, related to the Lowes are you, John? There were Whitehouses in his family tree.
Barmouth is a wonderful place to visit if you have the opportunity - it's one of the most picturesque towns I've ever seen.
Penrallt, where Lowe spent much of his childhood, is still there. It commands a spectacular view of the Mawddach Estuary and railroad bridge into town. The seamen's mission in the town has items connected with him, as does the small town museum (which has certain opening hours - you might want to look into this). The school he briefly attended there is still standing. From memory, one of the pubs also has (or had) a few items referring to Lowe. Unfortunately the Pavillion picture palace where the presentation was held for him following the Titanic disaster has been torn down and replaced with an amusement arcade. The churches where he and his brothers sang in the choir are still standing though - one commands a magnificent view of the town.
His grandfather's house in Egylrhos, where he was born, was demolished long ago. However, the house he lived in for many years after his marriage, Bryn Mostyn, was still standing in Colwyn Bay last time I visited, but it was unoccupied and derelict. I'd have to check if the Council Chambers are still there. When you go across the Conwy Bridge, you may be interesed in knowing that Lowe chaired the committee responsible for its construction for a while.
Deganwy is still somewhat as it was in the last years of his life and a lovely place to visit, but there's a lot of new development going on there that some locals fear is changing the character of the place.
Of course you can visit the grave where Harold, his wife and the ashes of his daughter are interred. It's in Llandrillo-yn-Rhos churchyard.
I'll give some thought to what else is still standing - PM me if you want more information on the locations mentioned above.