Designing a Sensory Garden on a Slope
We don't always have a nice level ground to plant a garden, so how do we make the most of sloped land when designing and building our sensory garden?

The only way to create flat surfaces when you have a relatively significant slope to work with is to add retaining walls and steps or stairs, thus giving your separate levels or "rooms" to work with. If done right, this can be a great opportunity to add interest to your garden.
Ensure that each level is flat and is connected by safe stairs or stepping stones.
A huge advantage of having multiple tiers in a single gardening area is that you can make each tier into its own "room." area. For example, you could have a room for different senses (sight, touch, hearing, smell, taste), or you can have exploring rooms and sitting rooms. You can even fence off "rooms" to make them safe places for kids to play and explore.
Try to design for some open spaces
As always, if you are choosing to add a lawn, make sure you do all the prep work. Don't just throw seed or sod on and hope for the best. As part of a sensory garden, though, consider how a lawn can be utilized to engage the senses. A lawn is certainly not ideal in all circumstances. Many locations are experiencing ongoing droughts and a more water-friendly solution may be best. Regardless of the material, a central open shape can emphasize color by other plants.
What to do with the retaining walls
Because you will need retaining walls to flatten the slopes, consider how you can incorporate them naturally into your room. If you want to make the retaining wall an asset, make sure it looks good and meshes well with the plants and other materials.
However, you can spend less money on the wall and just plan on covering them with flowing vines or other plants. Do you want plants that will soften the look of the walls? What senses are you planning to engage? Again, having these unique elements, such as retaining walls and steps, can be used to your advantage.
A place to sit
You will need a place for people to sit. All sensory gardens need a place for people to sit and ponder, pray, or do whatever works best for them to experience peace and healing in the garden. Having one or more comfortable, yet sturdy, benches will encourage people to take their time in the sensory garden.
Consider the possibilities
You can find that your soon-to-be garden is on a slope and feel frustrated, or you can utilize terraces to take advantage of the land. Tiered gardens have many possibilities and allow a lot of room for creativity.