How would I demolish a large wall blocking a tunnel?

I've tried using a sledgehammer, and that didn't work. I didn't try very hard though. I think it is constucted using concrete blocks. How would I destroy it? Would I require explosives? I don't know what to do. What would you suggest?

I feel I should add that there is limited room to work - this wall is actually about twenty feet down the tunnel.

Is that you making all that noise under my bank...?
If so then please stop it...you're scaring my lions.

Start at the bottom middle,Hit one block at a time.Destroy it.Then work upwards.

Hire a Kango (heavy duty hammer drill). That'll do it xxxx

get a masonry saw with a water hook-up...make some relief cuts and whack away with the sledge...

My approach would be to create a small hole in the centre of the wall to allow me to inspect the state of the tunnel from there, then decide to proceed or not.
With a hired SDS drill,l I would drill out the mortar between the blocks and then use the drill as a chisel (most of them have a rotary stop to allow chisel use), and remove a block that way, once a hole is created, demolishing the rest becomes so much easier, even with your sledgehammer.
Be careful, wear goggles.

I doubt you will be allowed to use explosives.... Hire a JCB/Backhoe....

Buy an old car out of the scrappy for about 拢50, then keep driving into the wall at high speed.
Granted it's not the safest option, but it's definitely the most fun.
If you want something a bit safer, go with the explosives.....

Do you know how thick the wall is? Can you remove any render to see what is underneath? If its 4-6" thick, I think you could then use one of those large masonary drills.
Drill a row of holes in a square (the size of one block) to weaken and then try and knock out the section. You can then see exactly what you're dealing with and knock through more of the wall.