Hi there. If you'd like to separate the closet, you could hang a tension rod and add a curtain in front of the opening. The fabric will add a decorative flair to the room and if you use ring clips on the rod it will slide open easily.
Hi Marj, to make the biggest impact and change to your guest room, I agree with Kim about adding a curtain rod and curtain to your open closet. You could make it look quite dramatic if you use ceiling to floor curtains over that area. If you have other windows in the room it might be good to use the same fabric for all. Depending on how much room you have under the bed you might consider cutting some boxes to slide easily beneath the bed for storing extra sheets, etc. I've done this in my homes. I paint the boxes so if they are visible at all (usually they're not) they look intentional. You can decide on the style you'd like for your guest room....quiet and serene by keeping everything neutral or vibrant and colorful by adding lots of designs and colors. Enjoy the project. Also, it also helps to spend a night or two in the guest room so you get to experience it as your guests would and then make an additional changes you feel would make it more welcoming. I like plants in my guest room.
I also had a closet like that and I also used the tension rods and I used really nice sheets to make the curtain since they are really light weight. It was a child closet, so I used two tension rods, one lower and one upper and had his everyday clothes on one level and better clothes on an upper level. That way he only had to open the curtain on the lower level instead of opening the whole curtain. It worked really well for him.
I have make a nice wall desk for my daughter which can help you to save quit a lot of space if you are dealing with a small room: https://www.youtube.com/watch?v=wy-_Oa8OLL4
Hope that it helps you