let me guess where you are: the lava river flows below and a room is above which you can't reach. There are some blocks which can be moved.
Pull the two blocks as far as you can so you can get behind them. There, climb the ledge where is another block, go behind it and push it. Now you can make the jump to the ledge which is quite far away, from there you can easily reach the exit - but beware the spiders.
Hope this helps.