  Tidal effects related to the traversability across thin shells are examined
in spherically symmetric geometries. We focus mainly on shells separating inner
from outer regions of gravastars (de Sitter -- i.e., $\Lambda>0$ -- interior
and Schwarzschild exterior of mass parameter $M$), but we also examine other
related geometries by including the possibility of a negative cosmological
constant and, besides, non trivial topologies where the shell separates two
outer regions. The analysis is developed for radially traversing objects and
for tides in both radial and transverse directions, which present difficulties
of somewhat different nature. Transverse tides are unavoidable across shells
which satisfy the flare-out condition, while shells in trivial topologies, i.e.
geometries with one asymptotic region, are more indulgent with the issue of
insurmountable tides. Besides, contradicting other cases analyzed in previous
works, we find that large radial tides cannot be avoided when traveling across
the shell in the gravastar solution, but in non-trivial topologies they can. We
study with special attention the traversability in practice of the transition
layer in the thin-shell gravastar solution. In particular, a finite object
which traverses radially the shell in a gravastar with $\sqrt{\Lambda}\ll 1/M$
undergoes a compression effect in both the transverse and the radial directions
due to the tides associated to the thin layer. The results are interpreted in
terms of the total momentum transfer obtained by integrating the travel time of
the object.
