1. Wormhole
There may be wormholes around the universe but outside galaxies. Here's how to make one:
1. Rip a hole in the universe.
2. Fill it with anti-matter.
3. Wait.
4. Jump in!
2. Extreme Speed
I don't mean that baby speed 600km an hour! I mean, going FASTER THAN LIGHT. You will need to go about 7,000 miles faster than the speed of light, any slower and you're going in a black hole. This will only allow you to get you to the future, but that still counts, right?
3. Cosmic Strings
These are inside the faults of the universe. Find a fault of the universe and grab 2 of the strings. They will distort time and space until time travel is possible, though be careful as one mistake and kabeeee goes the universe.
4. Building a time machine
I can't explain all of the steps, sorry

5. Kerr holes
They may exist but however the closest one is very far away. However their pull isn't infinitely strong, so you won't look like an vegetable that has been thrown into a blender millions of times.