The Amazon River flows endlessly through northern Brazil.

Literal

Amazon-river [topic-は] endlessly north-Brazil [obj-を] flowing [progressive-ている].

延々と 'endlessly / on and on' is an adverb emphasizing continuous extent. 北ブラジル 'northern Brazil' — a geographical proper noun. 流れている is the progressive of 流れる 'to flow,' marking the river's ongoing, permanent state. A clean geography sentence.