Où = when, where (in the context of a relative clause, however, où can be translated as "that").
Jour de fête = holiday
Tu t'amuses = Second person singular, present tense indicative, of s'amuser, "to have fun."
L'endroit = the place
Tu te sens = Second person singular, present tense indicative of "se sentir, "to feel."
le plus libre, la plus libre = the most free.