A stupid, yet very interesting question

[[vL]Kp]

Thanks for these tips ! How can we know if we have achieve the proper character level ? Only by trying to enter directly or is there another way to know it ? We're both level 16 at this current moment.

You could look it up in Jarulf's Guide, of course. It's the definitive source for answering factual Diablo questions.

Catacombs: 8
Caves: 13
Hell: 17

Also, note that Nightmare difficulty requires clvl 20 to join (but you can then go anywhere once inside), and Hell difficulty requires clvl 30. Beware that there is a Hell region and a Hell difficulty; the 17 refers to the region, the 30 to the difficulty. Blame Blizzard for the confusing nomenclature.