Highland is the neighborhood right across the platte river from lodo.
to the guy living on 20th and arapahoe, I had a buddy who lived on 21st and arapahoe, at a place called monkey mania.
carry a knife or gun at night. I've been robbed in that neighborhood before, its sketchy as fuck.
el chapultapec is an awesome dive, as suggested above. if you like real seedy, try out bar bar, probably the biggest shit hole in denver. the 404 club on broadway is nice for a cheap beer and great food. if you're on broadway, an obvious choice is the hi-dive, and there are some other great bars right in the area. if you go north a bit, two great well known spots are the larimer lounge or the walnut room, which serves 2 dollar pitchers of pbr on tuesdays. one of my favorite bars is Streets of London, great times there.
I'll post a more detailed guide later, I'm late for work