Life isn't easy for short people, as Grounded shows us. Getting into the incredibly isolated sandbox biome is going to take quite a bit of effort on your part. But it is worth it, a laboratory is there, as well as new objects.
The picnic table
It is certainly possible to construct buildings high enough in order to enter the sandbox in your own way. But that might take a lot of effort. It is comparatively simpler to take the path intended by the developers. This path involves climbing onto the picnic table, to begin with.
To sum it up:
- Drop the shovel on the southwest corner of the table with explosives.
- Go through the left plank to reach the other bench.
Knock off the cooler handle with a level 2 hammer.
Once on the table, join the Research Station, at the back is a zip line.
You now need 12 Silk Threads to repair the cable of the zipline , which will allow you to reach the sandbox in a fun way.
Once in the sandbox, it may be wise to build a makeshift base in the opposite corner, since there are materials, water, and a research station there.
The sandbox biome is very hostile, especially during the day, you will be roasting in the sun, which requires taking refuge in the shade. Using the Protective Cool Mutation can greatly help you survive, especially at level 3. The lion ants that are in the sandbox will also ambush you. Finally, you need a level 2 shovel to fully exploit the area.
To leave the sandbox, there is no miracle, you have to use the Daredevil Mutation and jump on a blade of grass. It may be possible to set up a zip line to descend to a destination of your choice.
In order to craft quite a few pieces of equipment and buildings, you need acid in Grounded. This is especially useful for the red chitin armor of ants. Here is a guide with a list of places and enemies to farm them easily.