The unification of quantum theory and general relativity remains one of the most important open issues in fundamental physics. A main problem is that we are missing experimental input at scales where quantum and relativistic effects coexist. Developing quantum technologies sensitive at these scales might also help answer other big questions, such as the nature of dark energy and dark matter. In this talk I will show how Bose-Einstein condensates (BECs) could be used to search for clues. These systems consist of millions of atoms cooled down to nano-Kelvin temperatures. A single BEC in a superposition of two locations could test if gravity induces the collapse of the wavefunction. Current experiments involve solids such as mirrors and glass nanobeads. In BECs atoms are not bounded as in solids, producing a variety of quantum states that might present advantages. I will also present a proposal to use Bose-Einstein condensates to access new spacetime scales directly. Applications include detecting gravitational waves at high frequencies, miniaturize devices to measure gravitational fields and gradients and set further constrains on dark energy/matter models.