We study the metastable behavior of diffusion processes in narrow tube domains, where the metastability is induced by entropic barriers. We identify a sequence of characteristic time scales $\{T_ε^i\}_{1 \leq i \leq \abs{V'}}$ and characterize the asymptotic behavior of the diffusion process both at intermediate time scales and at the first critical time scale. Our analysis relies on a refined understanding of the narrow escape problem in domains with bottlenecks, in particular on estimates for the exit place and on the conditional distribution of the exit time given the exit place, results that may be of independent interest.