Here are some cool themes to lay the ground work for you maps. 
Ancient Ruins
Have your players explore ancient ruins. They could collect research from the ruins or maybe they got there completely on accident and are now being attack by plants. Its up to you. 
This theme can be paired up with almost every single other theme. The ancient ruins theme is also a very good way to create lore.
(Example: My FOREUNNER has an ancient alien race that has gone extinct however the remnants of their civilization can still be found on many planets.)
Space Investigation
Ever since GIMKIT creative was made there have been maps based on the GIMKIT mode ONE WAY OUT. Now to play on that idea you can create a story where a group of GIMS investigate a spaceship to uncover its secrets. You could even add an onboard AI that can give hints using a button, command table, and a popup.
Moon Base
I dont see people talking about this but for those who dont know there is a type of terrain called the space rock. The space rock terrain is the moons surface. So why not make a moon base using this type of terrain.
Survival Island
A popular theme among GIMKITers is the Survival Island. There are many things you can do with this theme such as, a battle royal, story, hide and seek. You can even pair this theme with the ancient ruins theme.
To add some spice to the beaches of the island you can even add some tropical palm trees!
Palm tree link:
How to make a good looking Palm Tree in Gimkit Creative (Difficulty 2/10 or 
)
Medieval Fair
With the new DLD update came a spike of new medieval style maps. To contribute to that here is a Medieval fair to put into some of your maps. Some additions you can add to your medieval fair are some food you can buy from the stalls or even a indoor circus section with minigames you can play inside. You can eve make a market place to sell items or to buy items.
[Circus idea by: @Blackfox45666]
[second picture and market place idea by @gimmaster12345]
Snowy tundra
Based on SNOW BRAWL and SNOWY SURVIVAL we have the Snowy Tundra theme. The Snowy Tundra is hopefully self explanatory but what it is just a snowy area. You can even pair this one with the Ancient Ruins theme, and if your feeling cool you can even pair this with the Medieval Fair to create a festive event.
To create the feeling of being in a snow storm you can add a no collision barrier on the top layer and color it white and set the transparency to how stormy you want it.
Under The Sea
This theme Is underwater. The main terrain you will use for this is the sand terrain. You can create the underwater affect by using blue colored barrier devices with no collision. An optional touch is water physics. when you enter the underwater area your speed is cut in half. however you can acquire an items that will put your speed back to normal. For the fish you just make a item spawner with fish and cover the bottom portion with a plant.
For even MORE details you can go check out this link by The_7th_dragon: How to make an underwater-based game - #72 by The_7th_Dragon
(theme concept and picture by max1. post inside of link by The_7th_Dragon
Infernal adventure
This theme is fire based. meaning your going to have to add that fire emoji 
. To make this as realistic as possible use the dark colored terrain to add that feeling that your surrounded by ash. For the lava use red plastic or Gray water with a red/orange barrier on top for a fiery effect use red barriers that have no collision on the top layer.
A game mechanic you can add to this theme is super heated rooms. These rooms will require your players to get an item or ability in order to progress through these rooms. To make the super heated rooms you will need invisible lasers that turn on and off every second. (you can stop using these after the first area to conserve memory.
(Idea and picture by @Aubec7 )
Old Forest
This Theme is really kind of a basic theme however that’s something about it that makes it so great. You can put limitless things in this them and most wont even contrast against it.
A gimmick that can go with this theme is ambush enemies, the way you incorporate this into your forests design is you get a bush, put the ambush enemy on top of the bush and then when the enemy ambushes you, you delete the bush to give the illusion that the sentry is jumping out at you.
To add to the effect of being in a forest you can add vines by putting upside down alien plants on trees, and if your players are in a dense forest you can make a no collision barrier on the top layer that is colored black and its transparency can be changed depending on how dense your forest is.
( Ideas by @Foxy and @Skeeter )
Dry Desert
I haven’t seen many maps use this theme even though this theme as a lot of potential. You could create thriving city, oasis, and even ancient ruins
For creating a desert themed ancient ruins I would suggest using R:221 G:178 B:85 on gray stone collums. For the ground just use brown stone.
For an oasis use some grass one layer above the sand and put some water in the middle of the oasis and you can even put some palm trees to add a little spice to your oasis.
Palm tree tutorial:
How to make a good looking Palm Tree in Gimkit Creative (Difficulty 2/10 or )
(idea by: @Here_to_help)
I may update these in the future. If you have any theme suggestions, type a reply below stating the theme, and a picture of you using the theme I will give credit and add them to the Post. You may also give me things to add to already existing themes, and I will also give credit for that.
Be sure to like to show if you found any of this useful, Have a wonderful day. 
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