My wife and I are long term San Antonio residents and casual cyclists. We had heard a lot about the Mission Trail and decided to check it out along with another couple on Mother's Day. To say the least, we were awed at what the city and the National Park Service has done for that stretch of the San Antonio River.
We rented our bicycles from the Blue Star Bicycle Company, conveniently located adjacent to the trail in a little area of shops and restaurants (which make a great place for "apres cycle" relaxing). The trail itself is completely paved and crosses back and forth over the San Antonio River via a series of bridges and low water fords. Since it follows the river, it has a gentle decline from the start to the end, which is Mission Espada. Of course, that meant that there was a gentle incline going back, but not enough to be overly challenging with basic rental 7 speed bikes.
The Park authority and City are reestablishing natural vegetation throughout the length of the trail to encourage wildlife and especially birds (we saw about 15 species of birds during our visit and we weren't looking very hard) since the river is located in the North American Central Flyway. While this is still a work in prpgress, the short term result is a profusion of wildflowers along the entire trail. It is one of the best wildflower shows we have seen in a state devoted to wildflowers in general. For that reason, I would recommend late March to late May as one of the best times to go. It is also not too hot that time of year which is nice because there is currently very little shade along the trail itself (although plenty nearby).
The other benefit of the trail is that it passes by all of the San Antonio Missions (except the Alamo) and their associated parks. Any one of these would be a great place to stop, sightsee, and even have a picnic lunch if you didn't want to take advantage of the numerous picnic tables situated along the trail. Those would also be good places to go if you needed a restroom facility since there are none on the trail itself (we're talking maybe a 5 minute detour here).
Our group took about 4 hours to complete the trail at a leisurely pace with a stop for a picnic lunch, although we turned around at mission San Juan Capistrano which is about a mile short of Mission Espada. That was because the trail is still being completed over that last stretch and we did not feel like riding a bike path in the street for tha last mile. However, if you wanted to stop and see any or all of the Missions, you could turn this into a full day experience.
In short, for a pleasant day, not too strenuous cycling, and a bit of local history, I would strongly recommend giving this activity a try.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.