Belvoir Castle Triathlon (Castle Race Series)
Grantham (Belvoir Castle estate), United Kingdom · July · Castle Race Series (Endorphin Sport ran it earlier)
Course: 1.5 km (0.9 mi) swim, 42 km (26.1 mi) bike, 10 km (6.2 mi) run. Organiser 2026 report: 1.5 km / 42 km / 10 km (0.93 / 26.1 / 6.2 mi); Racecheck lists 40 km (24.9 mi). Olympic is on the second day with the Gauntlet.
Why people love it
- Racecheck averages 4.32 of 5 from 114 reviews, with staff scoring 4.79.
- Starter (200 m (656 ft) / 220 yd) and super sprint options for newcomers.
- Race through the Belvoir Castle estate; 2026 lake water was 21.9 °C (71.4 °F).
- Sprint is 750 m (2,460 ft) swim, 23 km (14.3 mi) bike, 5 km (3.1 mi) run (820 yd, 14.3 mi, 3.1 mi).
Watch out for
- The organiser calls it one of the toughest in the series, with a hilly bike and run.
- Weedy, shallow multi-lap lake swim; Racecheck water quality scores 3.78 of 5.
- Roads are not fully closed and one reviewer reported cross traffic.
- Rough ground leaving T1; reviewers suggest trail shoes for the run.
- 2025 was wet and slippery, so plan for rain.
Race
How racers feel about it, how well it is run, and how it treats a first timer. Counts for 30% of the overall score.
Toughness: Very tough
- Racer satisfactionLoved4.0
Racecheck averages 4.32 of 5 from 114 reviews, held back by weed and congestion complaints in the lake. · Medium confidence
- OrganizationWell run4.2
Racecheck rates staff 4.79 and navigation 4.68, with notes on a bottleneck at the T2 exit and cross traffic. · Medium confidence
- First timer friendlyDoable2.7
1.5 km (0.93 mi) multi-lap lake swim, hilly 42 km (26.1 mi) bike and a trail-like 10 km (6.2 mi) run. · Medium confidence
Course traits, not part of the score
- PR potentialAverage2.6
2025 winners 2:21:55 and 2:51:19 over a hilly course. · Medium confidence
Swim
Wetsuit odds, water temperature, calm, and the experience of the start. Counts for 16% of the overall score.
- Wetsuit legalUsually4.3
2026 water was 21.9 °C (71.4 °F) and 20 °C (68 °F), just under the 22 °C (71.6 °F) wetsuit ban. · Medium confidence
- Water temperatureComfortable4.3
20-22 °C (68-72 °F) in 2026. · Medium confidence
- Calm waterGlassy4.5
Estate lake, ideal water conditions both days in 2026. · Medium confidence
- Swim easeModerate2.8
Longest multi-lap swim in weed. · Medium confidence
- Swim experienceFine3.2
Racecheck Water Quality 3.78 is lowest; weedy, murky, slimy; but castle backdrop. · Medium confidence
- Swim supportGood3.8
Lake with lifeguard and kayak cover, shallow enough to stand in places. Multi-lap congestion was reported. · Medium confidence
Bike
Road surface, closures, scenery and wind. Counts for 18% of the overall score.
- Road surfaceGood3.5
Estate and country roads; no surface complaints found. · Low confidence
- Road closuresPartly closed2.5
Reviewer reported cross traffic and road-safety concerns; not clearly closed. · Medium confidence
- Bike sceneryBeautiful4.2
Racecheck reviewers call the bike scenic; castle estate roads. · Medium confidence
- WindSome wind3.3
Hilltop estate; no wind reports. · Low confidence
Course traits, not part of the score
- Bike speedAverage2.8
Hilly with a 2024 athlete saying also fast. · Medium confidence
- Bike flatnessHilly2.4
Demanding climbs over the 42 km (26.1 mi) bike. · Medium confidence
- Bike simplicitySome technical parts3.0
Twisting circuit after a climb per a sprint preview; cross traffic and a T2-exit merge flagged. · Medium confidence
Run
Crowds, aid stations, conditions underfoot and scenery. Counts for 13% of the overall score.
- Crowd supportStrong3.6
Small and intimate (55% of reviewers) but festival weekend with 1,300 athletes (2026). · Low confidence
- Aid stationsGood3.6
Racecheck Aid Stations 3.82, lowest category score after water quality; reviewers want non-water options. · Medium confidence
- Run sceneryBeautiful4.3
Scenic estate trails per Racecheck. · Medium confidence
- Run conditionsModerate2.7
Mixed surfaces. · Medium confidence
Course traits, not part of the score
- Run flatnessHilly2.4
Hilly 10 km (6.2 mi). · Medium confidence
Conditions
Air temperature, how predictable the weather is, setting, and spectating. Counts for 13% of the overall score.
- Air temperaturePleasant3.9
July in the East Midlands, about 15 to 24 °C (59 to 75 °F). 2025 was wet, 2026 sunny. · Low confidence
- Weather reliabilityVariable3.0
2024 sunny, 2025 repeated downpours, 2026 sunshine and rising heat. · Medium confidence
- Venue beautyStunning4.6
Castle estate and lake setting. · Medium confidence
- Spectator friendlySome viewpoints3.4
Large estate; lake and finish area accessible but courses spread out. · Low confidence
Course traits, not part of the score
- Low altitudeSea level4.8
About 90 m (295 ft). · Medium confidence
Stay and travel
Hotels, walkability, getting there, and the town around the race. Counts for 10% of the overall score.
- Hotel availabilityBook early3.0
Rural; Grantham and Melton Mowbray have limited stock on a festival weekend. · Low confidence
- Hotel valueNormal3.3
Not documented. · Low confidence
- WalkabilityWalkable3.5
Festival village; a 400 m (437 yd) uphill run from lake to bike racks in the 2024 super sprint. · Low confidence
- Travel easeOne connection2.7
Remote estate about 60 km (37 mi) from East Midlands airport; A1 and Grantham station about 10 km (6 mi). · Medium confidence
- LogisticsSimple3.6
Racecheck Logistics 4.59; multi-race festival with a merge at the T2 exit. · Medium confidence
- Town and foodFine3.0
Rural; Grantham and Belvoir village; festival food on site. · Low confidence
Key facts
- Location
- Grantham (Belvoir Castle estate), Leicestershire / Lincolnshire border, United Kingdom
- Typical month
- July
- Organiser
- Castle Race Series (Endorphin Sport ran it earlier)
- Field size
- About 1,300 athletes
- Distances (non-standard)
- 1.5 km (0.9 mi) swim, 42 km (26.1 mi) bike, 10 km (6.2 mi) run
- Swim venue
- Belvoir Lake on the castle estate (open-water lake, described as horseshoe or M-shaped; multi-lap because water is shallow farther out) (lake)
- Water temperature
- 20–22 °C (68–72 °F)
- Wetsuit
- Legal
- Swim start
- wave
- Swim laps
- multiple
- Key climbs
- Hills on the estate roads (organiser)
- Run shade
- Some
- Air temperature
- 15–24 °C (59–75 °F)
- Humidity
- Moderate
- Altitude
- 90 m (295 ft)
- Nearest airport
- East Midlands (EMA), 60 km (37 mi) away
- Where to stay
- Grantham, Melton Mowbray, Nottingham
- Booking
- Rural: Grantham, Melton Mowbray and Nottingham have hotels; camping and on-site options for the festival weekend.
What racers and reviewers say
- Racecheck (Belvoir Castle Triathlon Series page)Raced 2026 · aggregator · Positive
114 reviews average 4.32 of 5 (4.41 in 2026). Reviewers agree staff and organisation are the strength (staff 4.79, communication 4.69). The lake swim draws mixed comments: weed, low depth, murky water and congestion on a multi-lap course (water quality 3.78). Bikes are scenic and hilly with some road-safety worries and a bottleneck at the T2 exit; runs are scenic, hilly and mixed-surface, so trail shoes are suggested. Aid stations are adequate but short on non-water options.
- Lincolnshire Online (Belvoir Tri Club at the multisport weekend)Raced 2024 · article · Mixed
Club members' accounts from the 2024 Endorphin Sport weekend. One athlete found the lake swim hard because of an M-shaped course. The same athlete enjoyed the hilly, fast bike. A super sprint athlete noted a long uphill transition run from the lake across a 400 m (437 yd) field. Another member did a first open-water race in a club suit while most wore wetsuits.
“The bike section was both hilly and fast”
- Belvoir Tri Club (club news)article · Positive
Club news says the Belvoir triathlon returned after a long break under new management, with several distances. Three members placed in age groups: Olympic 2:52:52 and 3:12:39, sprint 1:30:13. Mentions no course or conditions comments; year not stated.
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Sources
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