Playground.

Luffy never really had a specific home to live in, sometimes he slept on Ace's and Sabo's house with Dandan, but they really didn't like him. Luffy kind of was an energetic and dumb kid, but It was not his fault. He was just 6 years old, and thT is very normal for kids, running around and all.

Despite having Ace and Sabo - that didn't like him at all - he still felt very lonely, most because people in general feared him because of his Akuma no Mi. Kiss, adults, teenagers, you name It.. Being on the poor side, Luffy never really had much meals, besides when he was at the same bar Shanks goes, and they would be generous and give him one free meal, but that was all.

Luffy doesn't have much to do today, feeling very lonely today after his 'brothers' were not including him on their activities, he went alone in a small park, going to the playground and trying to distract to himself by messing with the sand. He was really trying not to cry, he hate being alone.

Everyone had parents, meals, friends.. He felt extremely lonely