2. Add a small sector off the main one. This will be the "wall" that opens up.
3. Now add a new sector off the second one.
4. In 3D mode, you should have a map similar to this.
5. Add a new texture for the "inside" of the wall (something that looks "rocky"). Move the floor and ceiling a little closer together.
6. In 2D mode, add two new vertexes to the wall sector
7. Now connect these points to split the wall into two sectors.
8. In 3D mode, slope the floor and ceiling of the two wall sectors to create a nice "hole".
9. In 2D mode add a sector effector sprite to each wall sector. Set the LOTAG of the SE to 13 and the HITAG to 5 (or some unqiue number that is not used with any other sector effectors in your map). Make sure the SE's point up -- this tells BUILD to close the hole when the map is loaded into the game.
10. In 3D mode, point at the wall next to the hole and press 'S' to add a sprite. Point to the sprite, press 'V' twice and select one of the crack textures. The crack will not stay here, it's simply easier to add it along a wall then to add it to the open space in front of the hole.
11. In 2D mode, move the crack to in front of our hole. Make the HITAG equal to the two SE 13 HITAGs (In this example, that would be 5).
12. In 3D mode, you should now have a crack "floating" in front of the hole.
