Esperanto: A Complete and Comprehensive Grammar/Adverbs

Adverbs
Adverbs in Esperanto take the ending -e. Examples of words in Esperanto that are adverbs include: flue, frumatene, senhalte, and senfine.

The accusative ending "-n" can occasionally be applied to adverbs to indicate the subject is moving in the direction indicated by the adverb. For instance: "Ili marŝis flanke" means "They walked in the flank", whereas "Ili marŝis flanken" means "They walked to the flank".