The Cypress Hills Provincial Park has excellent riding based out of the Elkwater Townsite, about 25 minutes south of the Transcanada Highway. With about 200m of elevation and some trails over 3 km in length, it gives a mountain riding experience hours east of the actual mountains. It is truly a gem for Southeast Alberta riders, and draws visitors from well into Saskatchewan.
Some of the longer trails that take advantage of the entire descent are multi user trails and it is important to watch for hikers and two way traffic. These are trails often based on old resources roads like Tower, Horseshoe Canyon, Mitchell Creek and Beaver Creek Trails. There has been some work done to make them safer and with easier and more sustainable slopes, with more work to come in the future.
There are some much more mountain bike specifc trails as well in the area, but all are also frequented by hikers so keep your eyes out. Too many greens to mention are available around the base area, but the Firerock area is worth exploring for some very fun and flowy machine built options. There is good connection between all the trails, but it can get a bit confusing so Trailforks is definitely your friend when trying to connect trails in the base area.
Moving to the top, there are a few trails that skirt along the top of the hills allowing for access to the above mentioned long, multi use trails without having to descend and ascend again to get to them. These relatively flat connectors are known as Mystery (both upper and lower) and Plateau trails.
Near the base of the tower (at the top of Hidden Valley Ski area) is a confluence of trails that are mountain bike specific. Last Grizzly is a downhill only black trail with fun berms, rollers and drops and is probably the most difficult trail in the park. If you are interested in a more gradual and relaxed way down, Cobbleminer is a green trail that snakes its way from top to bottom. Mazama Drop is a handbuilt blue flowy trail that goes from the top to the bottom in 2.5 kms and an elevation drop of almost 200m. Or gain if you like going up hills. It also has a short connecting trail to Cobbleminer called Tephra, which is a fun, flowy time.