Well you're right on doing the agility course. Bring an anti-poison and some food like monkfish's or cakes or whatever you wish in your inventory. Wear mage-def armour such as d'hide for slight protection against Rev's (assuming you do this in non-pvp) or weight reducing armor such as spottier cape and boots of lightness. You can also bring a familiar, the best one being the terrorbird because you can use it to store more food and use the scrolls to keep running. To get there teleport to Ardy and head west to the wildy teleport lever, be sure to bring a slash weapon. After you're teleported run west past the mage arena until you reach the course. Open the door and you should automatically try to cross the ledge.