The Oil and Gas Discovery Centre is, by some distance, the most worthwhile thing to do in Seria. Funded and operated by Brunei Shell Petroleum, it was built to demystify the industry that built this town — and it succeeds. The exhibits walk you through the full lifecycle of oil production, from geological surveys and seismic exploration through to drilling, extraction, and refining. The science is explained clearly, the interactives actually work, and the whole place is well maintained.
Do not be put off by its corporate origins. This is not an advertisement — it is a proper science museum that happens to be about petroleum. Families with children will get particular value from it: there are plenty of hands-on exhibits, and the scale models of offshore platforms and drilling rigs are impressive. Entry is free or low-cost, and it is air-conditioned, which matters in the Bruneian heat.