Subarachnoid space ends at

The dura and arachnoid along with the subarachnoid space containing CSF extend up to 2nd sacral veebra. Below the lower border of L1 and S2 veebrae, the subarachnoid space contains 40 spinal nerve roots of L2-L5, S1-S5 and Co 1 which constitute the cauda equina. Ref: BD Chaurasia's HUMAN ANATOMY, Volume 3.