Shambala and Lamar are pretty close to each other, so as far as distance from the ruins it's the same.

Most people take a cab, or rent a bike, or walk.

Very few of the small hotels run tours to the ruins. Most people go on their own or get one of the authorized tour guides at the gates to the ruins.

Shambala is about 1.5 k south of Posada Lamar, which is, in turn, about 5.5 k from the ruins. You'll end up driving there or taking a taxi either way. If Roberto at Shambala arranges tours, you could consider that, or you can just go to the ruins early in the day and hire your own guide.

Hit the ruins first thing in the morning, as soon as they open, and check out the beach below the ruins, maybe meander over to the beach road and hit the beach again there, check out the various hotels along the way, but back to the road at La Vita e Bella or Mezzanine (the one that's up on the cliff) and walk south a little ways until you get to Mayan Grill (formerly Nacho's) and enjoy a leisurely lunch with one of the greatest views going. Then call a taxi to take you back to your hotel so you can take a beach nap there.

Just my two cents for a nice single day in Tulum.

Oh, and Lamar does not run tours. I'm sure Myrna would try to put something together if you asked her, but they don't really do tours.