How to break concrete below the ground

I am attempting to take down an old, rusted set of monkey bars. The bases are cemented into the ground. The cement is too large to dig out. I am trying to break the cement with a sledge hammer and am not getting anywhere. Any ideas?

I am thinking of cutting the posts down as low as I can and covering them up with more cement, but I would prefer to remove the posts.

Thanks in advance for any assistance/ideas anyone can provide.

Welcome CMin:
You can rent an electric jack hammer, start at an edge and give it what-for.
Glenn

Another option would be to buy the freedom of a car jack from the trunk of some car at your local auto wrecker for $1. Drill a hole through the steel post and attach a chain to the post with a long bolt. Put a concrete block on one side of the cement footing about a foot away from the pipe, and put a short piece of 2X4 on that nearer block. Place another concrete block about 3 feet away from the cement footing. Put a short piece of 2X6 and a car jack on the further concrete block. Buy two 2X4's, cut both in half and glue and screw those pieces together with PL Premium construction adhesive to make a 3 1/2 by 6 inch by 4 foot long beam. Loop the chain over the beam and rest one end of the beam on the 2X4 on the nearer concrete block and the other end on top of the car jack. Now you have a car jack that can lift 1000 pounds easily pushing up on a lever with a 3:1 mechanical advantage, so you can lift with well over 3000 pounds of force. I'm just guessing that this would be enough to pull that concrete footing out of the ground.

I'd also try just keeping the chain super tight and waiting for the ground to move and gradually let go of the footing. Try tightening up that chain every day and see if the footings will gradually pull out of the ground.

PS: I'd use a scizzor jack, and start with it in the almost fully raised position where the mechanical advantage is the greatest.

Also, you should be aware that concrete (and all masonary materials) are very strong in compression, but very weak in tension. That means that you should never put anything heavy on a concrete block unless that block is oriented the way it normally is in a concrete block wall. I've seen people "put a car up on blocks" but the blocks were oriented vertically (presumably for greater height so that someone could work under that car) and the car's rear axle was resting on the end WEBS of two concrete blocks. That means that the weight of the car was trying to bend those concrete webs, and that meant that the bottoms of the webs would have been in tension. I ended up knocking on that persons door and told someone's wife how dangerous that situation was, and that it would be much safer to use two concrete blocks oriented normally where each vertical block was. For $10 they could easily correct that situation.

Concrete blocks should only be used in their normally installed orientation. Otherwise, they can be surprisingly weak.

I have a similar situation in my backyard. The previous owners left an old swingset which has its arms set into a slab.
Since I never specified its removal as "one of the things to do" before we closed on the house. . . we now have a free swingset. Oh well, that'll teach me.
I guess I'll try renting a jack hammer. If that doesn't do the trick, there's always dynamite.

This How to Break up Concrete - wikiHow article\wiki-how might be useful.

@superjedi; Dynamite is a little to Tim the Toolman Talor-ish

you could always tie a rope to the top bar &, using a come-along, ropes & pulley, or the wife's car, pull the damn'd thing out of the ground, & then slice it up into manageable pcs,,, good luck !