I think every marriage goes through some times of boredom or lack of spice but there are things that you can do to spice it up. Being married almost 30 years, I have experienced the lulls at times but my wife and I have always managed to find things to do to bring it alive again.
Some things you can do that do help are:
Have a date night and keep it low key but romantic. Maybe a movie and a nice dinner at a semi-fancy restaurant. You don't need t go over board for the same effect.
Spend time in bed reminiscing about how you met and what you did on your first few dates. Maybe even talk about how you explored each other in the beginning. These things do bring back feelings that kicked off the relationship and it brings you to feel those feelings again.
Try some new sex games. There are board games out there for lovers that can be quite fun. Make up your own and the winner gets his or her choice of a sex act.
Depending on your relationship, this may or may not work, but I know some people have tried it and enjoyed the results while others did not. I am talking about bringing someone else in to join the two of you for a threesome, or a foursome. Unless you are really secure in your relationship, you might want to skip this.
Use your imagination to try new things and have fun doing it. That will keep the spark alive. Good luck and have fun.