Amenity Supply and Sustainable Underground-Space Vitality in a High-Density Commercial Interchange Hub: Evidence from Licun Station, Qingdao

High-density commercial interchange hubs are important components of transit-oriented urban regeneration. However, high passenger flow does not necessarily generate sustained underground-space vitality. This study examines the Licun high-density commercial interchange hub in Qingdao, China. It explores how amenity supply influences sustainable underground-space vitality through user behavioral responses. Based on 426 valid questionnaire responses, an amenity evaluation system was developed across five dimensions. These dimensions include natural-environment, facility-and-service, consumption-experience, socio-cultural, and transport-connection amenities. The entropy weight method was used to identify the perceptual differentiation of amenity indicators. PLS-SEM was then applied to examine the pathway of “amenity supply–user behavioral response–underground-space vitality.” The results show that natural-environment amenities present the strongest perceptual differentiation, while facility-and-service amenities play a fundamental role in supporting user behavioral responses. Consumption-experience amenities promote visit choice, stay duration, and satisfaction, but may weaken interaction and participation, indicating a potential tension between commercial vitality and public interaction. Transport-connection amenities mainly affect visit choice rather than sustained use. Among user behaviors, stay duration, interaction and participation, and satisfaction feedback are positively associated with underground-space vitality, whereas simple visit choice is not. These findings suggest that sustainable vitality in a high-density commercial interchange hub should not be understood as passenger volume alone. It should be understood as the transformation of transit flow into voluntary stay, interaction, satisfaction, and repeated use. This study contextualizes amenity theory in a high-density commercial interchange hub. It also offers planning implications for underground-space regeneration.