What did thoreau mean by his references to the “ruts of tradition” and “castles in the air? ”

Thoureau wanted to poit to the fact that following traditions limits us and deprives us from developing our imgination. Thoreau, like other romantic authors, does not agree with tradition.  He thinks it prevents people from finding true greatness and blocks their path to spirituality. "Castles in the air" are simply illusions by which people persuade themselves in something that is not true, in Thoureau's opinion.

there were abundant sources of fuel nearby