the closest thing to the experience of space travel 
(ROOT (NP (NP (DT the) (JJS closest) (NN thing)) (PP (IN to) (NP (NP (DT the) (NN experience)) (PP (IN of) (NP (NN space) (NN travel)))))))
(ROOT (NP (NP (DT ) (JJS ) (NN )) (PP (IN ) (NP (NP (DT ) (NN )) (PP (IN ) (NP (NN ) (NN )))))))