。
I feel like dancing in the field.
Literal
Field [at-で] dance-[desiderative-たい] feeling [copula-です].
~たい気分だ is a common pattern for expressing a current mood or inclination — 'I'm in the mood to X.' Uses the desiderative ~たい attached prenominally to 気分 ('mood, feeling'). Softer and more atmospheric than the bare ~たい.