Minecraft server ideas?

Try adding some custom mobs to your worlds. I would suggest MythicMobs. It's a free plugin and finding help on how to do things is easy (there is a manual, an entire help forum, and Youtubers are constantly uploading videos). Or, another idea...try creating a redstone device. Not like an automated door, but something like recreating a song with noteblocks or creating a changing maze (like in Maze Runner) for when day and night change.