It's not necessary and it's incorrect. לשם means "to there". You are going somewhere to travel in there, you are not traveling to there.
Actually, I had the same confusion as AniKelly - it is possible for the (English) sentence to imply traveling to somewhere as well: "Do you like going to China?" "Sure, I travel (to) there every chance I get." Obviously it's necessary to get to "there" first...and then, presumably, one would also travel in "there". I guess that's where לנסוע comes in, huh? " אני נוסע לשם ואז אני טייל שם " ?? But if לטייל means to walk or hike, couldn't one use it to say "I hike (travel) to the top of those mountains every weekend."?
I thought "הן מטיילות" meant "they hike" or "they stroll" or "they wander around" more than "they travel."