Atlas stone is a great way to improve your strength. You can make one at home and train like a strongman.
P.s: I'm not a native speaker, so sorry if i made any language mistakes...
Step 1: Equipment
This Atlas stone is made out of a PVC fishing float. I get mine for free at a port as some fisherman thrown it away. I'm not sure how much it's cost, probably around $10-$15 from some online store i found. You also need an angle grinder, a drill, hole saw drill bit.
Step 2: Make It Round...
Use an angle grinder to cut these parts and grind it off. Be careful! The plastic will get hot, and release toxic gas. Remember to wear a face mask.
Use a hole saw drill bit to create a hole. Around 45mm+ is good enough to fill.
Now you have many options. You can use a PVC female threaded and a threaded cap to make a seal after filling. Here i use a cap from an empty bottle. Put it through the hole and use super glue to stick it in place.
Step 5: Finish
And that's it. You can fill it with sand or rock. The float is 400mm in diameter, so it would be 0.0335 cubic meter volume. Therefore it can hold 50kg of beach sand. That's a good amount of weight.
It's better to keep the cap upward when it's full filled, just in case.