1. Sweet and Nasty

Celebrating Halloween in all its dirty debauchery is as easy as venturing over to Adams House for the infamous Sweet and Nasty Masquerade Ball. And don’t fret, unlike during its absurdly exclusive daytime hours, Adams Dining Hall is accessible to all for this costumed dance party. Enjoy platforms, poles, cages, and prizes for the first 50 guests. Leave the sweet for the trickor-treating teens and get nasty.   10 p.m.-2 a.m., Friday, October 30, Adams Dining Hall, $5.

2. Scare in the Square

Don’t be alarmed if you blearily stumble out of your dorm Friday afternoon to find yourself face-to-face with a menacing monster or a milky-faced mime. It’s just Harvard SCARE, the Square-wide party where magicians, monsters, and mimes overtake the streets of Harvard Square in preparation for the subsequent “Monster Mash” block party, featuring games, contests, evening entertainment and maybe even some spooky surprises.Festivities start at 4 p.m., Saturday, October 31, Harvard Square, Brattle Street. No admission fee.

3. Howl-O-Ween

Be a part of a burgeoning Boston Halloween tradition and head over to Faneuil Hall to watch the “Howl-O-Ween” Pet Parade. Pets will be costumed in their very best ghoulish get-up, promising a devilish dog and fur-eaky feline festival.  10 a.m.-6 p.m, Saturday, October 31, West End between Faneuil Hall and Quincy Market Building.

4. Go Frightseeing

Despite the words of our 8th grade history books, the rich history of colonial Boston is not all tempestuous tea parties and triumphant Revere rides. Board the “Trolley of the Doomed” and be prepared to shiver and shudder as the deepest, darkest secrets of Boston’s earliest disease-ridden days are exposed. Don’t be surprised if New Haven suddenly seems a lot a less frightening...Departs every half hour from 7-9 p.m., all week long. Old Town Trolley stop #1, downtown Boston, $37.  Reservations required.

5. Must-See Macabre Movies

Cinematic classics you secretly cherish are celebrated. The Coolidge’s 9th Annual Halloween Horror Marathon features a range of films, from “The Blob” (1988) to cult classic “Night of the Creeps” (1986).Doors open at 11 p.m., Saturday, October 31.  $10 double feature, $20 marathon.