I too have reached the temple and I think basically at this point its a tough ride. To unlock the Temple shortcut the third item is a key from the Mines. So you have to first find a key in one of the Mines levels (don't think its guaranteed each run through since I've done many runs of the whole Mines without finding one) and then take it with you all the way through Mines/Jungle/Ice Caves to the awaiting Tunnel Man, without dying of course. And that is by no means easy.
Carrying the key everywhere puts another dynamic on your playstyle. You will likely end up relaying the key back and forth throughout the levels, hoping that it doesn't either fall on you and kill you, or you lose it (either somewhere like the ocean floor levels or the dark levels). Makes the dark levels even tougher as you are juggling torch carrying with managing damsels/weapons/key.
Basically harder than Dark Souls, but very addictive.
XBox Live, Origin and Games for Windows Live Gamertag: teamHAM