Why does Ender feel at home in the lake?

Ender feels at home in the lake because it gives him the same feelings he had at battle school. He'd spent four years of his life training..... and it felt like home.

"The strong part comes from Battle School. The sunbrowning comes from this lake. I spend a lot of time on the water. When I'm swimming, it's like being weightless. I miss being weightless. Also, when I'm here on the lake, the land slopes up in every direction."

"Like living in a bowl."

"I've lived in a bowl for four years."