Peaceful Warrior: Master Self-Defense with Calm Precision

UndergrounD Fitness & Self Defense:
The World’s First Montessori Martial Arts Academy
Click below to join our VIP text club and get a free week of classes! 

Introducing UndergrounD Fitness and Self-Defense

Your Premier Montessori Martial Arts Experience - Online or in Jacksonville

Experience the world’s first Montessori Martial Arts Academy with UndergrounD Fitness and Self-Defense. Our innovative curriculum integrates martial arts with self-defense techniques, tailored for students from age 3 and up. With two locations in Jacksonville, FL, we offer both in-person and online classes to fit your schedule. Our seasoned instructors emphasize a safe, personalized learning experience, empowering each student to excel. Seeking to enhance confidence, physical fitness, or self-protection skills? UndergrounD Fitness is your destination. Embrace your potential today — call us at (904) 704-7888 or click below to join the VIP text club!

Strength and Mobility

Our classes are all great for increasing strength and mobility with fun and engaging exercise.

Discipline and Focus

Our martial arts family strives to instill discipline and focus in every student and in every lesson.

Meet Your Montessori Masters

Meet Jacksonville’s Renowned Martial Arts Instructors – Master Christopher Williams (left) and Master Benjamin LaMasters (right)! With 50 years of combined expertise, Masters Williams and LaMasters are committed to imparting their extensive knowledge and fervor for martial arts. Join our community and experience the transformative journey of martial arts under their guidance.

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Years Combined Experience

minja class

Minjas (Age 3-6)

Development of fine and gross motor skills. Character development such as sharing, respectful words, discipline, and confidence. Growth of executive function (doing the right thing at the right time). Available online or in person.


Soft Training Tai Chi

Good for the Elderly/Mobility Impaired. Increased range of motion, flexibility, balance, and coordination. Breathing and stress relief techniques. Internal organ strength and development. Basic mediation skills. Available online or in person.

children's class

Children (Ages 6-12)

Development of fine and gross motor skills. Character development such as sharing, respectful words, discipline, and confidence. Growth of executive function (doing the right thing at the right time). Available online or in person.


Private Lessons

1 on 1 coaching with our Masters. Personalized guidance on your fitness or martial arts program. Lessons will be tailored to your individual goals. Character development on skill, confidence, and discipline. Available online or in person.


Adults (13+)

Increased range of motion, flexibility, balance, and coordination. Self defense tactics that are safe, simple, and effective. Alternative form of exercise that still includes weights, resistance, and cardio movements. Available online or in person.


Unleashed Fitness

Stand alone program or works with our Montessori martial arts. Increase strength with weights. Improve cardio and endurance with professional coaching. Available online or in person.

Ready to get started?

Join our Martial Arts Family!

Online Only

  • Unlimited Weekly Classes
  • Access to Curriculum Videos
  • Quarterly Rank Evaluations
  • Materials Mailed to You (shipping not included)


  • Unlimited Weekly Classes
  • Access to Curriculum Videos
  • Quarterly Rank Evaluations
  • Standard and Family Style Classes Available

Personal Training

  • 45-minute Lessons (online or in person)
  • 3 Training Sessions Per Month
  • Focused on Your Desired Skills
  • Access to Curriculum Videos
Get a free week of training by joining our VIP text club! 

Martial Arts are not "One Size Fits All"

Our Montesorri methods ensure that everyone learns at their own pace and in a valuable and comfortable way. Be sure to communicate your goals with your instructors, we can customize your training to meet those goals! 

The Benefits of Montesorri Martial Arts

Integrates physical, mental, and emotional growth.

Focuses on personal improvement, not team competition.

Encourages setting and achieving personal milestones.

Breaks down complex techniques into manageable steps.

Central to martial arts, enhancing focus and discipline.

Helps with spatial awareness and motor skills.

Allows expression of energy in a controlled, respectful manner. 

Promotes respect and positivity among peers.

Makes learning exciting and boosts self-esteem. 

See what people have to say with the testimonials below!

Underground Fitness is amazing.  The instructors are professional, relate beautifully to children (and adults) of all ages, and they consistently go the extra mile to make sure all their students have the tools they need for success.  Our children have been students of these instructors for almost 10 years now, and we couldn’t be happier to have followed them to their opening of Underground Fitness. If you are looking for a place where your child can build confidence and mixed-martial-arts self-defense skills, this is the place!


I'm very grateful for the work the karate instructors have provided for all the kids my daughter has adhd and since she started karate, she has shown great improvement in concentration. They also took the extra mile and brought professionals one mental health and one dietitian. I just wanted to say thank you for the patience and the hard work on my daughter.

Omar A.

We love being a part of the Underground family! My 6-year-old son started with them a few months ago, and has already moved up one level. He is now SO proud of himself, and we are proud parents as well! Master Ben and Master Williams are great with the kids, and they aren't only teaching Taekwondo and fitness, but life skills such as self control, focus, respect, and teamwork. The option of the online classes is wonderful as well, we love when our son tells us he wants to take extra classes online in addition to his weekly in-person class. It's great to see our son coming out of his shell more outisde the home, and taking pride in his activities, and we thank Underground for the part they have played in that!

Bettiann B.

THANK YOU for the Women's Self-Defense Seminar! It was, extremely, informative, engaging and entertaining! I took away, many, valuable skills that I could use, to protect myself and/or someone else if found in a dangerous situation. I, highly, recommend all women take part in this training as it helps to overcome fears, build confidence, sense of empowerment and freedom. I look forward to the next session!


My, 8yr old son, who has Autism and severe language delay, is doing amazing in this class! Though communication and comprehension is very difficult for him; both, Master Williams and Master LaMasters are extremely patient and understanding! I love how they connect with him, in a way that he can understand, and he is treated/included the same as everyone else. I am completely amazed at how much he has learned and grown, beginning on day one. Can't thank you enough for all you do! I, highly, recommend Underground Fitness and Self Defense to everyone!

Kizzy J.

Amazing would be an understatement for UndergrounD. The masters so incredibly great with teaching on different levels to ensure everyone understands, learns and has fun. My daughter gets so excited for her classes and they have helped tremendously with her self confidence, bravery, manners and respect. They teach so much more than hits and kicks- the things they teach is what shapes these children into amazing human beings. Can’t say enough great things about this place- highly recommend!

Heather K.

Our 4 year old is thriving in this class. He is an active young man and this class matches his energy and it is teaching him respect, kindness and understanding all at the same time. Master Ben and Master William have the perfect balance...making class fun and teaching the lessons to make my son respectful, kind and a confident young man. I would recommend this class to anyone.

Madeline B.

Absolutely love Master Williams and Master Ben. They are so patient with my son (4 yo) and work so well with kids. My son looks forward to “ninja training” every week. They are so good at teaching and being serious about martial arts but keeping it fun at the same time. Highly recommend!!

Taylor F.
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