There are three major routs to get to the entrance of the Sigiriya garden, from West, North or South. The most commonly used entrance is the West entrance.
If you take the conventional route, you would gain entrance though the West gate and exit through the South gate where the current car park is. Should you choose to walk from the Sigiriya road, through the south side and around the rampart to the West gate to the garden, you would be able to comprehend the architecture of the Sigiriya Garden. You can buy tickets to enter the Sigiriya museum, the garden and the rock from near the west gate. You can drive up to the west gate but I preferred to walk.
The inner moat. You may wonder what happened to the outer moat. Well by the time you come to the see the inner moat you have already passed the out moat and the outer rampart without noticing it. Only the most keen and watchful eye will capture these details without a guide bringing them to your attention.