New observational methods often trigger new discoveries in astronomy. To explore the universe in an innovative way, we are constructing a multiple telescope system named the 7-dimensional telescope (7DT) at the El Sauce Observatory in Chile. 7DT is made of twenty, 0.5-m diameter wide-field telescopes. Ten of the 20 units have been installed and started taking the data, with the expected completion of the full system in 2024. With 7DT, we will perform the 7-dimensional sky survey (7DS), a wide-field, time series, spectral mapping of the southern sky. The survey aims to (i) understand the spectral variability of astronomical sources through time-series spectral mapping such as active galactic nuclei; (ii) provide a spectral map of the sky that can be used to study spatially resolved stellar population of galaxies, cosmology, etc; and (iii) rapidly identify electromagnetic counterparts of gravitational-wave sources for successful multi-messenger astronomy. In this talk, we will introduce 7DT and 7DS and outline the unsolved problems that 7DS will tackle.