浩瀚 (hàohàn) is a literary, emphatic adjective for 'vast, boundless' — used for oceans, deserts, the universe, or figuratively for someone's breadth of mind. It is stronger and more poetic than 广大 (broad in area or number) or 广阔 (wide, open space), and unlike 茫茫 (which adds a sense of indistinctness or confusion), 浩瀚 simply stresses immensity. 无穷 (endless) is a verb/adjective for time or quantity, not physical space.