WELCOME TO SOUTHIE

Mass Underground is excited to announce the opening of our second location on East 1st & K Street in South Boston! Memberships are now available for purchase.

JOIN NOW

Book your tour to see the space!

We recommend new members book a walk-through tour to see all that the space has to offer. During your tour, you will have the option to stay and get in a FREE trial workout on us!

Book Now

SOUTH BOSTON MEMBERSHIPS

YEARLY

For the best deal, commit for 1-year!

$129/Month- Billed Monthly

6 MONTHS

Option to join for a 6-month commitment.

$149/Month- Billed Monthly

MONTHLY

Not ready for long-term? Join our monthly membership!

$179/Month

JOIN NOW

INCLUDED AMENITIES

Every Mass Underground, Southie membership includes access to all of our cardio equipment, machines, free weights, saunas, ice baths, lockers, and facilities.

Your membership grants you access to our South Boston location Monday-Sunday, 365 days.

🎥 POV: We’re more than barbells and big lifts.

We wanted to make sure we were building a space for all kinds of movement- from heart-pumping cardio to slow, intentional stretching. This space was inspired by one of our owners (and her baby bump!) to make sure everyone feels at home here, no matter how they move🖤

Natural light. Open floors. Quiet corners to breathe. Because your gym should fit every season of life.

#bostonfitness #southboston #southie #workout #workoutwithus #bostongym #movement #massunderground

New merch just dropped⚡️ Limited quantities available for presale now through Thursday. Grab yours before they’re gone! Can’t wait to see you all repping 💪

[Shop Now / Link in bio]

The Summer of No Gatekeeping: Top 3 Favorite Machines

1️⃣ Reverse Hyper- @westsidebarbellofficial
2️⃣ Lateral Raise- @arsenal_strength
3️⃣ Plate Loaded Fly- @arsenal_strength

Just our personal favorites we keep coming back to!
Drop your favs in the comments👇

#bostonfitness #westsidebarbell #arsenalstrength #lifting #weightlifting #southie #southboston #reversehyper #lateralraises #plateloaded #massunderground

Summer is officially here and we are kicking it off by celebrating 1 Month of having our doors in Southie OPEN!☀️

It’s been a wild ride and we are so thankful you all are along for it with us. Here’s to longer days, harder lifts, colder plunges, and plenty of cold brew 🏋️❄️

#bostonsummer #summer2025 #bostonfitness #bostongym #southie #southboston #workouts #massunderground

We opened in Southie because it felt familiar.

The energy. The grit. The work ethic. The roots.
It reminded us of why we started Mass Underground in the first place.

No gimmicks. No fluff. Just a community of people who show up, train hard, and take care of each other. That’s what we’re about- and that’s what Southie is too.

This neighborhood has history- our history- personality, and pride. We’re proud to be part of it🤝

Thank you all for the warm welcome.
We’re just getting started🚀

#southboston #bostonfitness #bostongyms #southie #workoutwithus #workout #massunderground

New here?👋 We’ve got answers!

From “can I come see the place first?” to “where do I check in?” - we’re breaking down the most commonly asked questions from new members (so you can walk in like you’ve been here once or twice 😎)

For specific questions about equipment and other policies, be sure to check out the posted signage at the gym, or ask us on your tour!

What other questions do you have? Let us know in the comments and we’ll be happy to answer them!👇

#boston #bostonfitness #newgym #gym #southie #southboston #workout #massunderground

Thinking about checking out the gym? You can now book a free trial/tour right on our website!

Come see what we’re about:
✔️Full weight room
✔️Cardio + machines
✔️Saunas + ice bath
(And other things like free cold brew bc why not?)

Come for a tour, stay for a workout- on us!

🔗 Link in bio to book!
📧 Email us info@massunderground.com if you need different accommodations
📸 @nolaneastmanphoto

#bostonfitness #gym #bostongym #fitness #oldschoolgym #modernamenities #boston #southie #southboston #massunderground

LAST CALL 🔐‼️

Presale pricing ends TOMORROW!
Join now = locked-in rates for life. (Yes, life.)

Still on the fence?🤔 Come by during our extended open house hours TOMORROW 5/2: 7–9am or 12–6pm and see for yourself!

Anyone who joins our exclusive presale will receive an MU hat or shirt, be kept in the loop on our opening day(!), and receive their discounted rate… forever ♾️

📩 DM us with any questions!

LINK IN BIO to join 🔗

#southboston #southie #bostonfitness #lifting #weighlifting #gym #newgym #massunderground

Fake candids, real gym 😃

Drop-In Open House Tours:
Monday–Friday, 7–9AM + 4–6PM, every half our on the half hour!

Drop in, look around, hear the spiel. If you’re looking for confirmation to join our presale, or if you’ve already committed- now’s your chance to see what we’re working with. Can’t make it? DM us, we’ll work something out. See you then!

#southboston #bostonfitness #boston #southie #lifting #workout #gym #openhouse #gymtour #massunderground

VIRTUAL TOUR 👀

In-person tour dates/times will be announced sooner than you think! Stay tuned for more info on when and how you can come see the space IRL. We can’t wait to meet all of you‼️

A limited number of discounted PRESALE memberships are still available- DM us with any questions!

#southboston #bostonfitness #liftinggym #saunas #icebath #weightlifting #southie #massunderground

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@fettlefitnessequipment
@thecoldlife
@roguefitness
@matrixfitness
@redwoodoutdoorsco
@arsenal_strength
@hammerstrengthofficial

📸 @petercano.video.audio

Plate by plate this thing is starting to look and feel EXACTLY how we dreamed it up. The countdown is officially on (stay tuned, it’s sooner than you think!) 🏁

#southie #bostonfitness #southboston #gym #comingsoon #boston #bostongym #massunderground

ZERO rest days😵‍💫 but worth every second! Could not do this without all of the physical, mental, and emotional support from this incredible community.

COMING (so) SOON!

#bostonfitness #southboston #gym #southie #workoutwithus #bostonworkout #massunderground

We are cruisin 🚀 Bathrooms and showers are coming to life- this not so glamorous, but absolutely necessary project is on its way to completion.. which means we’re one day closer to opening our doors 👀

#bostonfitness #southboston #opengym #liftinggym #southie #gymlife #gymdemo #workout #massunderground

Weights and lifting equipment are a given, but we’re fired up about our cardio plans too😮‍💨

What are you most pumped about? Tell us!👇

#bostonfitness #boston #southie #gym #cardio #liftinggym #southboston #massunderground

SNEAK PEAK👀🔥🥶

Our space is changing quite literally everyday and we could not be more excited about all of the progress that’s been made so far!

🔜 Stay tuned for more updates (including when/where we’ll be opening!)

#southboston #southie #bostonfitness #gymrenovation #gym #fitness #sauna #icebath #comingsoontoboston #comingsoon

Making moves and clearing out the mess so we can open our doors ASAP, Southie!🧹

🎥 Shot & Edited: @petercano.video.audio

#bostonfitness #southie #southboston #bostongym #demoday #painttransformation #comingsoontoboston #comingsoon

Nothing like a delivery day in the middle of winter to remind me I chose a career that requires heavy lifting before the workouts even start. Thankful for all of the mental and physical support 🚛💪

New equipment is in now from @arsenal_strength thanks to @jordanclarke.ak (and some unpaid family volunteers)😏

#GymOwnerLife #WhyDidIDoThis #BostonFitness #Southie #SouthBoston

Big things happening at the Southie location throughout the next few weeks 🚧

Follow along for behind-the-scenes updates while we build this thing from the ground up🔥

#southbostongym #bostonfitness #lifting #gymlife #southie #boston #gymdesign #massunderground

One month ago we walked through with a vision💭

Follow along to see where we’re at- and where we’re going 🚀

#massunderground #bostonfitness #boston #gymowner #buildout #renovation #gyminspiration #southie #southboston

Exploring our new neighborhood🍀
We can’t wait to lift with you, Southie 🔜🏋️

#SouthBoston #MassUnderground #BostonGym #Lifting #BostonFitness #Fitness #Southie

The Next Episode ✔️

Southie📍
Spring 2025

#southboston #southie #bostonfitness #bostongym #comingsoon #opengym #massunderground #boston

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@massunderground.southie