After you've melted the ice enough to enter the Cenote, simply make your make to the back and climb the stairs. There will be a tablet there along with a box. Inside of the box is a blueprint that will allow you to see the hidden keys. Once you've constructed the chip, equip it and go out into the world and start looking for the keys. From a distance you will see a gold shimmer. As you approach the shimmer it will quickly take on the form of the Warden's altar with a box on top of it. Inside of the box is a key. There are 13 in all but you only need 10.

1. 1895 : 75 : 266
2. -1433 : 118 :555
3. -1328 : 91 : 1325
4. -382 : 28 : 1495
5. 2375 : 97 : 1009
6. 1435 : 75 : -758
7. -925 : 88 : -627
8. -303 : 84 : 614
9. 1586 : 51 : 560
10. 714 : 67 : 1709
11. 1316 : 7 : 1503
12. 1536 : 22 : 2219
13. 1257 : 17 : 249

Some players are having problems with the concordance, however, a follow gamer has made a map should help you in case you need a map view.

Big thanks goes to Cyberscooter

https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=3227860584

You will not be able to use the keys until you've completed terraforming the planet so don't bother looking for the keys until that point but you most certainly can collect the keys as you are exploring and building.

When you have at least 10 keys, follow the instructions on the tablet in the Cenote and this will give you and alternate ending. If you enter the Cenote at the earliest possible time, 32GTI if I remember correctly, and construct the chip as quickly as you can, you will most likely find most, if not all of the keys before terraforming is completed, but if not, that's why I created this guide.

If this guide helped you, please leave a like and I'm happy that it helped.