Help finding book about trip to center of universe and one other book


Sep 13, 2012
Married with one son and five (Yes, 5) lovely gran
I'm looking for titles and authors for two books.

Book one has a spaceship finding a wrecked liner in space with but one passenger left. He is this ageless life form that if I remember correctly somewhat resembles a turtle. They agree to add him to their crew and seek the center of the universe. I wish I could remember more but its been years since I( last read the book. Any help would be greatly appreciated.

Book two has a couple of young men of Amerindian decent, one of whom was named Dakota, meeting two girls and then going together to find out what is happening with a problem near a mysterious mountain. There is an city there protected by a force shield or a barrier of some kind. The trouble is a monstrous life form under the control of an evil guy from the city who has a way to go in and out of the city to the outside world. Again, any help would be greatly appreciated.