Dungeon Crawler

Do all dungeons need to be completed, or entered? Or can we just go to the altar?

And, does this include castle dungeons?

You just need to visit the altar room, not complete, clear, or enter the dungeon. And I'm not sure if this includes Castle Dungeons since I visited them just in case.

That's what I'm currently doing. Don't have castles yet, so doing them anyway :U

Yeah, I think this journal achievement is glitched. Can anyone confirm? I've visited every dungeon altar, along with all 3 arenas, and all 3 hardmode dungeons. I only went on the altars, though.

That should be good enough, have you tried making a check off list, writing down each and every dungeon and arena, then visiting them one by one checking it off as you go? You may have missed one and not noticed. After you try that and if you still don't have the achievement, you can send Nexon a ticket on their website and they'd hopefully fix it. (Also, I'm pretty sure Hardmode dungeons don't count, but I may be wrong.)

I'm like, 98% sure I've visited each one, but I guess I'll try again. I've ran through them all 3 times now.

I don't think you need to go into castle dungeons. but you can just enter the lobby and leave, unless I'm missing something. I got it just now just simply entering Peaca's Dungeon Lobby.