diablo 1 question?

Yes, there is. However it is difficult to get there in singleplayer games. If you want to get to a higher difficulty level, you need to make a multiplayer character and get it to level 20 to create nightmare games or level 30 to create hell games. You do NOT have to kill Diablo to get into higher difficulties, it is based entirely on character level. Unlike in Diablo II, multiplayer characters in Diablo I are stored on your computer rather than on battle.net, and you can play a multiplayer character solo in a cable or modem game without even having to connect to any other computer. After you get your multiplayer character high enough to create a game in a higher difficulty, they say that if you create such a game, then exit back out and play your singleplayer character, it too will be in a game of that difficulty (although again, presumably only if its level is high enough). However, I would recommend playing multiplayer characters anyway as you can take them onto battle.net if you want and it's also easier to play in higher difficulties.

Note that there are differences between playing multiplayer and playing singleplayer. In multiplayer, there is no load game, and anything that happens to your character is more or less permanent. This means that you MUST NOT touch an ornate, fascinating or sacred shrine, and you MUST NOT touch a goat shrine or a cauldron just in case it's an ornate, fascinating or sacred shrine (I would highly advise that you keep backups of your characters in case you do touch one of these 'booboo' shrines). Also, in multiplayer the quests are different. Rather than being random, only a few quests are available: The Butcher, King Leoric, Archbishop Lazarus, and Diablo. These are always present in every multiplayer game. Additionally, there are no secret levels; King Leoric is found standing around on level 3, and Lazarus has his own little room in the upper quadrant of level 15 (the Butcher and Diablo are accessed in the normal manner). If you die in multiplayer, rather than being forced to reload, you will have to restart in town, naked and with 1 health. In order to get your items back, you will need to go back down to where you died and pick them up off the ground. In case there are still monsters around where you died, it is a very good idea to keep some secondary equipment around to use for retrieving your primary items. I would recommend that your multiplayer character be a sorcerer, as sorcerers are much tougher than warriors or rogues and generally have a much easier time retrieving their items after they die.