Located near seaside context and rich natural ecologies of the mangrove beach of Bangkok’s outskirt - Bang Khun Thain, Habitia-H Club facilitates a recreational function as a clubhouse and a gateway entrance for a housing estate “Sansiri”. Habitia-H Club is a one- storey building situated in a 1,750-square meter site area with a 302-square meter floor area. The owner’s requirement is to create the architecture demonstrating an impressive impact with the combination function of a leisure center and a main gateway. How to design and combine these two different characteristics of space between private and public, indoor and outdoor; be- comes an interesting condition that need to be solved with a new approach of concept design. To cope with a problem of space arrangement, the architects experimented the concept of plane twist and derived with a huge simple twist shape, which can answer all the limitations. However, the construction was the most challenging process. The technique using reinforced concrete casting with GRP panels (Glass reinforced plastic) was employed to create the smooth curvilinear structure. Inspired by gentle curve of the beach along the mangroves forest context, the architects design a concrete shell structure serving as an entrance and clubhouse of the housing estate transforming the building into a curvilinear form. The facilities of this building include a living area, a swimming pool, and a fitness room. An open-plan arrangement with the inside out approach allows the nice ventilation and the qual- ity of semi-outdoor space. A reflection pool helps create relaxing atmosphere and expand the vision and perception of the users. The characteristic of wooden stakes in the coastal area was employed to use as the landscape elements and columns in an interior space as well as pillars for the metal lattice cov- ering the terrace. An interesting shape and form of the seashore plantation like mangroves was carefully selected to create a pattern of the carbon steel square tubes. This part of steel struc- ture uses metal lattice to create a quality of transparency for the semi-outdoor area and trans- form it into a functional and interesting space. The lighting design concept derives from the inspiration of fireflies. Since a large group of fireflies represent how abundance of the mangrove forest, this idea was employed to repre- sent the richness and plentifulness of the project. At night, metaphorically, the light glow under the concrete shell transforms this building into a hive of fireflies. Moreover, creating the different ambience, the building allows sunlight penetrates into the shell in daytime and the interior light spot lighten up the shell at night like the hive of fireflies. The design presents an iconic expression for the otherwise functional architecture of the housing estate’s gateway entrance and leisure club.