。
I went to visit my grandma's place.
Literal
I [topic-は] grandma [of-の] house [object-を] visited [explanatory-んだ].
The verb 訪ねる takes を for the place visited — like English 'visit X.' The colloquial ending ~んだ frames this as explaining or sharing context, often as response to a question or as conversational lead-in. おばあちゃん is the affectionate, casual form of 祖母 ('grandmother').