Adjectives

(s)brooding, broody, contemplative, meditative, musing, pensive, pondering, reflective, ruminativedeeply or seriously thoughtful“Byron lives on not only in his poetry, but also in his creation of the ‘Byronic hero’ - the persona of a brooding melancholy young man”
(a)reflectivecapable of physically reflecting light or sound“a reflective surface”
(s)reflectivedevoted to matters of the mind“the reflective type”