Complex sentence: Martha enjoyed an upbringing of unbridled wealth and privilege, living between the Allan family mansion in Montreal's Golden Square Mile, Ravenscrag, and "Montrose", the Allans' summer house at Cacouna.
Split into simpler sentences: Martha enjoyed an upbringing of unbridled wealth and privilege. She grew up between Ravenscrag, the Allan family mansion in Montreal's Golden Square Mile, and "Montrose", the Allans' summer house at Cacouna.