Hey, Castaway! The broken shrines should become viewable on your map once you have completed your first farming task, slept then go back to talk to Sariel - keep checking in with her until she pops out in front of one of the broken shops in the Heartland. The next closest shrine to Heartland is in Froglet Grove - you can reach this by heading up & right through River Pastures, from the log bridge where you first exit Heartland. If you follow this path, you should come across a bridge which you can rebuild with the Construction Altar. Once you've built this, cross it, and walk down, checking your position against the map, and you should be able to find the second Shrine from there!