One of the hard to reach areas in Sonic Frontiers is 1-7 on Kronos Island. Check out this guide to find out How To Get To 1-7 In Sonic Frontiers. This way you can get some more keys to help you unlock more Chaos Emeralds.
How To Get To 1-7 In Sonic Frontiers
In order to get to 107 you will have to complete a puzzle. Head here on the map and you will see some switches you can hit.
You are trying to make a rail to get to the other side. The first switches should look like this. Move the green pieces and then hit the switch.
This will create a rail to another smaller island. There is another puzzle here. You need to make a cross rail that you can use on your way back. Move the green pieces again and then hit the switch.
Take the rail back and then jump on the cross rail to get to the level. It might take you a couple of jumps, but this is how you can get there. Now you can gather up some more keys before heading to the next area.
Check back soon for more Sonic Frontiers guides.