Studies of extreme cases within quantum mechanics have always been particularly attractive. How macroscopic can objects be and still demonstrate unique quantum features, such as entanglement? What are the real limits of measurement precision in quantum mechanics? I will review our experiments where macroscopic objects are driven deep into the quantum regime. Observation of a quantum trajectory in a quantum reference frame with, in principle, unlimited accuracy will be presented. A concept of a reference frame with an effective negative mass required for such observation will be introduced. Sensing of magnetic fields and of mechanical motion beyond standard quantum limits of sensitivity using this concept will be presented. Application of those ideas to gravitational wave detection, continuous variable quantum repeaters and e.-m. field sensing will be reported. References Hybrid quantum network for sensing in the acoustic frequency range. Novikov et al. Nature 643, 955 (2025). Entanglement between Distant Macroscopic Mechanical and Spin Systems. Thomas et al. Nature Physics 17, 228–233(2021). Overcoming the Standard Quantum Limit in Gravitational Wave Detectors Using Spin Systems with a Negative Effective Mass. Khalili and Polzik, Phys. Rev. Lett. 121, 031101 (2018).