Quantum effects you can observe
with your own eyes:
Boiling liquid helium (4He) over and below Tλ = 2.17 K.
The dramatic differences in the boiling (many gas bubbles and liquid turbulence if T>Tλ but no bubbles at all for T<Tλ) have their explanation in that in the superfluid phase the quantum effects are observed at macrocospic scales: the thermal conductivity of the liquid in this suprefluid phase is so large that all the evaporation takes place in the liquid (superfluid)-gas interface. In addition, any of these two photos constitutes a "visual" manifestation of Heisenberg's Uncertainty Principle: in spite of the so low temperatures the helium does not solidify, due to the "zero point energy". (Photo obtained in the students lab of Cryotechnology and Critical Phenomena of the Faculty of Physics, University of Santiago). For further details, see F. Vidal, La constante de Planck a escalas macroscópicas: superfluidos y superconductores. Revista Española de Física 14, 77 (2000).